Meta-aminobenzoic acid: Structures and Spectral Characteristics

This article was downloaded by: [Palafox, M Alcolea] On: 15 December 2010 Access details: Access Details: [subscription number 931246444] Publisher Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 3741 Mortimer Street, London W1T 3JH, UK

Spectroscopy Letters

Publication details, including instructions for authors and subscription information: http://www.informaworld.com/smpp/title~content=t713597299

Meta - Aminobenzoic Acid: Structures and Spectral Characteristics

M. Alcolea Palafoxa; M. Gilla; J. L. Núñeza a Departamento de Química Física I (Espectroscopía), Facultad de Ciencias Químicas, Universidad Complutense, Madrid, SPAIN

To cite this Article Palafox, M. Alcolea , Gill, M. and Núñez, J. L.(1996) 'Meta - Aminobenzoic Acid: Structures and

Spectral Characteristics', Spectroscopy Letters, 29: 4, 609 — 629 To link to this Article: DOI: 10.1080/00387019608007055 URL: http://dx.doi.org/10.1080/00387019608007055

PLEASE SCROLL DOWN FOR ARTICLE Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article may be used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material.

SPECTROSCOPY LETTERS, 29(4), 609-629 (1996)

-

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

META AMINOBENZOIC ACID: STRUCTURES A N D SPECTRAL CHGRGCTERISTICS key words: meta-aminobenzoic acid, scaled frequencies, vibrational spectra, AM 1, geometry optimization, atomic charge.

M. Alcolea Palafox, M. Gil and J.L. NGfiez Departamento de Quimica Fisica I (Espectroscopia). Facultad de Ciencias Quimicas. Universidad Complutensc. Madrid 28040. SPAIN.

ABSTRACT

Two conformations of minimum energy (I-syn and I-anti)were found in metu-amhobemoic acid by the Ah41 semiempirical method. All the geometric parameters were optimized and compared with published data obtained by means of X-ray difhction. The dipolar form of metuaminobenzoic acid was also optimized by AM1 . The vibrational spectra were computed in all cases. Several scale coefficients were used to improve the theoretical spectra. The total atomic charges, the electronic density and several thermodynamics parameters were also calculated. INTRODUCTION

Metu-Aminobenzoic (m-aminobenzoic) acid belongs among the

fundamentalmolecular skeletons used in physical organic chemistry. This compound, depending on the nature of the solvent, the phase or 609 Copyright 0 1996 by Marcel Dekker, Inc.

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

610

ALCOLEA PALAFOX, GIL, AND NUREZ

preparation of the sample, may to be found in either or both of the molecular forms: neutral and dipolut. M-Aminobenzoic acid exist predominantly as a neutral molecule in non polar solvents and as a ,witterion (or dipolar form) in the solid state or in aqueous solution'-z.In the case of the neutral form, the cahoxylic group is somewhat disordered; the molecules are connected by hydrogen bonds between the carboxyl groups of the two different molecules in the asymetric unit, as a cyclic dlmer type. rn-Aminobenzoic acid has a wide-spread variety of interesting pharmacological and biological applications, with a structure-activity relationship close to the behaviour of para- and ortho- isomers'. T h s compound is a chemical substance whose contribution in synthesis of analgesics, anthpertensives, vasodilators, and other drugs is well-known. Quantitative analysis of structure-toxicity relationship4,antitumoral activity in mouse s k d , chemical repellency6, inhibitory action in plant growth', and a extense number of biochemical or cellular determinations versus m-aminobenzoic acid' have been evaluated. The role of this compound in the chemical passivation of iron, steel9*,and aluminium9bin aqueous solutions has been reported. The chemical shifts and acid-base tautomeric equilibria of marmnobenzoic acid have been stuhed by Cahon-13 NMR spectroscopy", and compared with the results obtained in other isomers and analogous compounds. The combined use of Carbon-13 and Nitrogen-15 NMR spectroscopy have permitted the identification of different molecular species: cation, anion and neutral rn-aminobenzoic acid in DMSO-d, and D,O solutions'&. The ionization mass spectrum has been obtained recently" establishing spectral differences with respect to ortho- and para- isomers. The surfaceenhanced Raman spectrum (SERS) of m-aminobenzoic has been plotted in the 3500-100 acid adsorbed on silver colloid cm-' range, showing their most intense bands. The IR spectra in the solid sfafe12.13and in the gas-phase'" have also been reported, but unfortunately only a few of their normal vibrations have been clearly assigned Theoretical calculations with the CND0/2 method'& and STO-3G basis set'& have been used in order to optimize the molecular structure of m-aminobenzoic acid. In the present paper, as part of a research program to determine the molecular structure and vibrational spectra of benzene derivatives, the values for m-aminobenzoic acid are shown. No experimentaldata are avadable on molecular geometry of this compound in gaseous or liquid phases.

META-AMINOBENZOIC ACID

611

THEORETICAL METHODS

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

The calculations were carried out by the AM1 semiempirical method", implemented in the GAUSSIAN 90 program packageI6. This AM1 method has shown a reasonable reproduction of the geometric parameters (bond lengths, bond angles and torsional angles)", the vibrational s p e c t r ~ m 'and ~ ' ~a~ remarkably wide variety of applications2&'' including studies of chemical reactions of various kinds. The geometry of m-aminobenzoic acid was completely optimized using the OPT keyword. Force-constant and vibrational frequency calculations were performed using the FREQ keyword. With all the geometric parameters fixed, the AM1 method implemented in the AMPAC program packageU with the PRECISE option, was also used to obtain the energy and several thermodynamical parameters.

EXPERIMENTAL The m-aminobenzoic acid was obtained from Fluka and purificated in the Calorimetry section of the "Instituto de Quimica Fisica ccRocasolano))", C.S.I.C., Madrid. Infrared absorption spectra of this compound in KBr pellets were recorded' in the 4000-200 cm-l range on a Perkin-Elmer 580A IR-spectrophotometer. A peakfinder program prepared in our Department and a interfaced W R D A T A 6/16 computer were used to read the absorption band frequencies. All measured band frequencies were vacuum corrected and they are believed accurate to f 0.5 cm'l.

RESULTS AND DISCUSSION GEOMETRY OPTIMIZATION At mom temperam the crystals of m-aminobenzoic acid are monoclinic with two independent molecules, A and B, both nonFor comparison purposes, Table 1 zwitterions in the asymmetric includes also the bond lengths and angles calculated from the X-ray difbction stuw,but these values are the average between the A and B forms. In parentheses appear the deviations of this averaged value. The optimized molecular geometry of m-aminobenzoic acid in the neutral and dipolar forms are given in Tables 1 and 2. In the case of the non-ionized structure, both possible planar conformations I-anti and I-syn are considered. The labelling of the atoms in the optimum conformation is plotted in Fig. 1, while in Fig. 2 is shown the dipolar form. In Table 1 it can be seen that for most of the geometrical parametem, the AM 1 calculations give very close values to those reported

ALCOLEA PALAFOX, GIL, AND NUNEZ

612

TaMe 1. Bond Lengibs (in mAminobenzoic Acid.

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

Lengths

c1 -c2 C2 - C3 c3 - c4 c4 - c5 C5 - C6 C1 -C6 c1 -c7 C2 - H8 C3 - H9 C4 - H10 C5-Nll C6 - H12 C7 - 013 013 - H14 C7 = 015 N11- H14 N11- H16 N11- H17 013 *-. 015 015 H14 -a*

and Bond Angles (in Degrees) calculated by AM1 for

NEUTRAL Conformations I-anti Csyn

1.4000 1.3932 1.3889 1.4183 1.4172 1.3941 1.4693 1.1006 1.1010 1.1002 1.3779 1.lo14 1.3671 0.9714 1.2365

1.3982 1.3937 1.3889 1.4185 1.4166 1.3957 1.4694 1.1002 1.1009 1.1001 1.3776 1.1019 1.3664 0.9715 1.2369

0.9852 0.9849 2.2074 2.2322

0.9853 0.9849 2.2079 2.2330

Dipolar

form

)(raya

1.3954 1.3988 1.3909 1.4080 1.4009 1.3963 1.5416 1.1056 1.1009 1.0991 1.4637 1.1067 1.2530

1.385 (0.006) 1.379 (0.001) 1.37 (0.005) 1.3945 (0.0035) 1.388 (0.007) 1.383 (0.002) 1.4805 (0.0005) 0.95 (0.02) 0.96 (0.01) 0.96 (0.03) 1.387 (0.008) 0.965 (0.005) 1.2815 (0.0045) 0.97 (0.03) 1.25 (0.004)

1.2584 1.0229 1.0256 1.0229 2.2551

0.89 0.91

(0.03)

in the crystal, although a certain extent of influence of intermolecular

interactions (e.g. formation of dimers) appear in the X-ray values. Similar to other semiempirical methods, the AM1 calculation appears to overestimate systematically the C-H and C-C lengths. In several bonds of the NH, and COOH groups, the comparison is difficult, because in the crystal lattice these groups strongly participate in the formation of hydrogen bonds.

META-AMINOBENZOICACID

613

Table I (continued)

Bond angles

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

c1 - c 2 - c 3 c2 - c3 - c4 c3 - c4 - c5 C4 - C5 - C6 C l -C6-C5 C 2 - C l -C6 C 2 - C l -c7 C6-C1 -C7 C1 -C2-H8 C3 - C2 - H8 C2 - C3 - H9 C3 - C4 - H10 C5 - C4 - H10 C4 - C5 - N11 C6 - C5 - N11 C5 - C6 - H12 C 1 -C6-H12 Cl-C7-013 C 1 - C7=015 01X7=015 C7413H14 CW11H14 CW11H16 CW11H17 H16-NllH17 H14N11H17 H14NllH16 a

From ref; 24.

NEUTRAL Conformations I - anti I - syn 119.14 121.oo 120.39 118.46 120.00 121.01 118.34 120.66 119.75 121.11 119.57 119.55 120.06 120.91 120.63 120.65 119.35 115.50 128.65 115.85 109.07

119.12 121.04 120.39 118.42 120.03 121.01 121.01 117.98 120.00 120.88 119.56 119.56 120.05 120.95 120.63 120.90 119.07 115.39 128.69 115.92 109.07

120.04 120.03 119.93

120.02 120.03 119.94

Dipolar

form 120.37 120.66 118.45 121.41 119.10 120.00 121.83 118.17 118.09 121.53 120.07 120.13 121.42 119.57 119.02 123.83 117.08 116.62 115.60 127.78 109.73 109.27 109.73 109.43 109.25 109.42

-

X-ray'

118.7 121.55 120.05 118.65 120.65 120.35 120.4 119.3 120.25 121.05 119.2 116.9 118.0 120.3 120.95 120.2 119.0 116.55 120.45 123.0 112.35

(0.2) (0.15) (0.05) (0.45)

(0.05) (0.05) (0.5)

(0.6) (0.35) (0.55) (1.1) (4.8) (0.2) (0.45) (0.7) (0.8) (1.35) (1.05) (0.3) (0.85)

118.45 (1.45) 114.95 (0.05)

l

ALCOLEA PALAFOX, GIL, AND NUNEZ

614

TABLE 2.

Dihedral Angles (in Degrees) calculated by AM1 for rnAminobenzoic Acid. ~~

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

Torsional anglesa

NEUTAL Conformations I - syn I - anti

Dipolar form

C2-C1-C7-013

180.0

0.0

0.0

C2-C 1-C7=015

0.0

180.0

-179.99

C6-Cl-C7-013

0.0

180.0

180.0

C6-C1-C7=0 15

180.0

0.0

0.01

C1-C7-013-H14

180.0

180.0

0.0

0.0

H14-013-C7=015

60.31

C4-C5-N11-H14 C6-C5-Nll-H14

-

-1 19.70

C4-C5-Nll-H16

-179.99

-179.94

-179.73

C4-C5-N 11-Hi 7

-0.05

-0.07

-59.75

C6-C!5-Nll-H16

0.02

0.07

0.27

C6-Cf5-N11-H 17

179.96

179.94

120.25

m e other torsional angles are 0" or 180".

A small ring distortion is calculated theoretically by AM1 in agreement with that reported by X-rap. By CND0/2 method, two conformations have been obtained'&with a pyramidal and a planar NH, group, but by AM1 only a planar NH, form was computed. By AM 1, the I-syn conformation is more stable (0.064kcal mol-I) than the I-anti form (by CND0/2'& this difference is 0.074 kcal mol-' with a planar NH,), in good agreement with the studies at STO-3G level'" reported in benzoic acids with other substituents (X= F, CH,, CN, NO,, ...), in which the syn forms seem to be the energetically preferred conformations.

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

META-AMINOBENZOIC ACID

615

I

- ant1

Fig. 1 I-anti and I-syn conformations of m-aminobenzoic acid and labelling of their atoms. The geometry corresponds to that obtained by AM 1.

ALCOLEA PALAFOX, GIL, AND NUNEZ

616

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

@

Dipolar form

Fig. 2 Optimum geometry for the dipolar form of rn-aminobenzoic acid using the AM1 method.

From non-ionized to dipolar form, Tables 1 and 2, the bond lengths and angles are in general observed slightly dependent on the structure, but the changes are remarkable in the region of ionization position. Thus in the dipolar form, the hydrogen bonded to 013 is in the amino group, and consequently, negative charge is concentrated in the OCO- group while positive charge is located in the NHjTmoiety. This h g h electronic density in the OCO group leads to bond lengths C7-0 13, C7-0 15 almost equal, and only ca. 0.02 A longer than a double bond; and a Cl-C7 bond remarkably longer (0.072 A) than in the syn or anti conformations. In the angles, the L 0 1 3 4 7 - 0 1 5 is greatly increased, 1 1.9", while L C 1-C7-013 angle changes only ca. 1.2". A small intramolecular interaction is established with the oxygens: 0 1 5 . H 12 (2.3405A) and 013--H8 (2.5029A) and therefore shorter L Cl-C6-H12 and L C 1 -C2-H8 angles, ca. 2", are computed.

META-AMINOBENZOIC ACID

617

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

Concerning the NH,' group, the N-H lengths are almost identical in the three hydrogens and slightly longer than in the NH, pup, ca. 0.04 A. The C5-Nll bond (as the C1-C7) is remarkably increased 0.086 A with the new atom on the amino group.However the C4-C5 and C 5 4 6 bonds are slightly reduced, 0.010 and 0.016 A respectively. The s u m of the angles around N11 atom is 328.1", sp' hybridization. In the dipolar form, the ips0 angle L C2-Cl-C6 decreases lo, while L C4-C5-C6 increases ca. 3" with regard to the non-ionized molecule. CALCULATION OF FREQUENCIES

The reliable prediction of vibrational spectra is of considerable use in assigning the normal modes in a molecule. The results obtained in some benzene derivatives using ab initio methods25za,semiempirical methods'*and noxmal coordinate analysi?' have been reported. To get the desired degree of accuracy in the prediction of a spectnun is not always possible because the experimental frequencies depend on effects that are not included in the theory, such as anharmonicity effects, Fermi resonance, intemlecular interactions, solvent shifts, etc. To correct this deficiency, sets of scale factors (or correction factors) have been reported in ab initioZa3Oand semiempirical methods" to be used on the computed frequencies. In the present paper, the calculations with m-aminobenzoic acid using AM1 method are carried out. Table 3 lists the vibrational frequencies and intensities calculated by AM1 in the I-syn and I-anti conformations, while Table 4 refers to the dipolar form. The vibrational modes are numbered according to the order of increasing frequencies. A one-to-one correspondence between the frequencies calculated theoretically and the experimental data obtainedIJ1 with infiared (IR) spectroscopy is established in Table 4. In this Table it is noted that the computed frequencies are systematically higher than experimental ones in agreement with AM1 calculated bond lengths which are expected to be longer than experimental. Such overestimation by AM1 is usually found with semiempiricalmethods1932J3. For comparison with calculated spectra (Fig. 3a), infrared spectrum from solid phase' is shown in Fig. 3b. The assignment shown in Table 4 is based on the frequencies computed by AM1 correlated by scale factors obtained !?om experimental

-

537 558 585 637 652 743 831 849 030 044

993 I079 I120 1153 1213

10 11 12 13 14 15 16 17 18 19

20 21 22 23 24

3.9 6.0 1.7 2.0 7.6

2.2 108.8 3.0 8.3 39.1 80.6 20.0 38.5 23.6 7.4

383 398 434 500

346

2.0 0.5 1.8 4.5 0.7 5.9 4.8 3.6 16.3

39 146 181 202

hbrolrbs (Km md',

1.2 1.9 0.5 0.6 2.4

0.7 33.4 0.9 2.6 12.2 25.2 6.3 12.0 7.4 2.3

0.6 0.2 0.6 1.4 0.2 1.8 1.5 1.1 5.1

R d h d

IR htermlly

705 806 909 923

1.0532

1.0532 1.OD7 1.0227

1.0373 1169

1.0222 971 1.128SC 956 1.0178 1100

547 729

427

217 422

1.0693 0.8741

0.9322

0.9322 0.8205'

d

F.da

sea*

I - syn confor ation

1 2 3 4 5 6 7 8 9

m') - -

Nc

3.9 6.2 2.1 0.9 9.7

1.5 108.4 2.7 8.1 36.8 80.4 14.8 38.6 25.8 5.4

537 556 580 637 657 743 832 849 930 944 994 080 120 157 204

0.5 0.6 0.2 4.2 0.4 12.5 5.8 0.5 15.3

37 145 180 202 345 401 398 418 500

Ab6om Km md'

4.49 1.63 6.70 2.04 6.33 4.21 6.30 1.40 1.60 1.60 1.66 2.35 3.22 1.51 1.14

1.2 1.9 0.6 0.3 2.9

8.37 4.19 6.03 3.04 1.04 5.52 2.52 5.23 1.90

0.5 32.6 0.8 2.4 11.1 24.2 4.5 1 1.6 7.8 1.6

0.2 0.2 0.1 1.3 0.1 3.8 1.7 0.2 4.6

RddlVO

IR InhWy

conformation

0.97 1.61 2.38 1.19 0.99

0.76 0.30 1.35 0.49 1.58 1.37 2.56 0.60 0.82 0.84

0.01 0.05 0.12 0.07 0.07 0.48 0.24 0.58 0.28

V(CH) 5 r(NHJ + U(CCCr 12 O(CCC) 12 (coupbd* I&)? + r ( N H j U(CH) 18b or 15 + r(NHJ O(CH) Qr

r(cooH) + r(NHJ + r(ring)' y(0H) + y(CCC)* 16. or 4 V(CCC) 6a + r ( c 0 o H r V(CCC) 4 AJCOOH) + U(CCC) 6b y(CH) 10b or 11 U(CCC) 12 + A(CO0H) + U(NHJ y(CH) 101 or 10b y(CH) 17b or 17. y(CH) 17r or 17b

r(c0oH) + T(NHJ + r(ring)' Ba? y(CCC) 16s r ( c o o ) + r ( N t i j + r*(ring)* y(0H) + y(CCCr 4 or 16a

v(CCC) 16b + v(NH3 -

T(COOH) + T(ring)'' + y(NHJ' Wing)' r(rlng-NHJs + r(co0H)

Characterization

TABLE 3:The FundamentalVibrational Frequencies and Intensitiesof m-AminobenzoicAcid (Neutral Form) calculated using the AM1 SemiempiricalMethod.

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

24.1 10.1 22.5 88.2 3.2 50.6 100.0 18.4 1.4

20.4 18.0 40.5 31.3 65.1

25.8

77.0 58.0 72.1 282.1 10.2 162.0 320.0 58.8 4.6

65.4 57.6 155.3 100.0 208.3

1504

1553 1638

1726 1754 1783 2075 3175 3180

3187 3195 3428 3553 3563

30

31 32 33 34 35 36 37 38 39

40 41 42 43 44

Related to line 37. Calculated v,,l contrlbvlion of thin mode.

--

isel

8.1

15.8 78.1 110.5

27 28 29

7.4

1.5 2.3 4.9 24.4 34.5

4.9

1237 1273 1322 1408 1435

26

25

v,

I L I

1.08 1.09 1.08 1.10 1.04

6.45 6.53 7.36 8.17 7.78

5.22 9.75 2.77 4.39 17.63 20.31 25.55 6.41 6.41

4.86

3.65 3.68 6.16 1.66 2.50 9.72 10.84 10.07 1.08 1.08

1.04 1.75 1.46 3.83 2.05

1.15 1.83 1.42 3.28 1.69

relation from benzene molecule (ref. 32). 'From ref. 19. 5According to nomendature used in ref. 19. *Very weak

-

1.0440c 3403 1.0263' 3472

20.0 15.6 45.6 20.2 63.1

38.1 23.0 17.2 72.0 3.7 46.8 100.0 3.4 17.8

7.2

1.5 0.4 2.0 29.9 26.3

-- - - -

66.5 51.Q 151.4 87.0 209.7

3185 31Q4 3429 3554 3583

1674 1587 1613 1600 3045 3049

1.0427 3056 1.0433 3082

1.0312 1.1051 1.lo51 1.2214' 1.0427 1.0420

126.5 76.3 57.0 242.3 12.3 155.6 332.3 11.2 59.3

24.0

1500 1560 1640 1681 1726 1751 1785 2077 3178 3179

4.9 1.3 6.8 89.4 87.5

1240 1277 1325 1404 1430

1.0654 1458 1.0654 1537

0.9844 1343 1.0451 1347

1.0373 1193

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

F

w

lo45 1101 1131

1011

954

523 586 608 650 745 703 835 945

48 135 164 198 372 394 415 487

ia

(Un.9

r

1.4 2.1 4.7 10.4 13.4 13.1 3.9 1.l 0.2 0.0

6.7 10.0 22.9 94.4 64.9 63.6 19.1 5.5 1. l 0.1

9.2 2.7 0.0

0.0 0.4 0.1 1.7 4.9 4.9 0.4 0.2 5.3

0.0 1.7 0.4 8.1 23.7 23.9 1.8 1.o 25.5

44.8 13.3 0.2

Rd€iWb

AbohAa

p n moc'l (a)

IR WMWV

793 024 933 Q80

1.0532 1.0227 1.0227 1.0222 1.0178 1027 1.M29 1056

696

1.0693 0.8741

548

522

0.9322

US&

423

(rn.')

F.dor

0.9322

subd FRpusncy

sub

2.0'

0.4 4.4 1.6

4.4 3.6

2.7

4.3'

(W

-

End

3.33 4.30 1.34

0.89 1.27 0.50

5.51 6.29 2.30 10.18 3.78 7.42 1.36 1.82 1.44 1.65 2.14 3.07 1.01

1.24 2.75 0.56 0.85 0.77 1.00

2.80

0.00 0.01 0.05 0.10 0.07 0.42 0.24 0.57 0.53

1.oz 9.58 4.98 6.53 3.05 5.11 2.61 5.61 3.78

-

[mDyndA)

M.ua (AMU)

ForCe

comturt.

Reducd

-- -

550m

442 m,bi 448s,b

-

R d . 31

1098Vw?

-

1 0 0 1 ~1007w

757821 m 790s 885w 918m 937w

r(OC0)+ r(ring)4+ T(NH;)

l(OCO-)+ T'(flIlg)* i'(ring)' t y(OCO-) T(ring-NH;)' + r(OC0) y(NH;) + y(CCC)16. r(--NH,')* + T'(OCO-)* v(CCC) 16b T'(ring)' + r(OC0)+ T(NH,*) y(CCC)16b + y(NH,3

w-47

Characterization

6(CCC)12 b(CCC)7b or 127 y(NH,') + b(CH)' 18s

6(CCC)60 + A(OC0-) + A(NH,') V(CCC)4 AJOCO-) + 6(CCC)6b y(OC0) + y(CH)11 759vs A,(OCO-)+ b(CCC)6b +A(NH;)' 856m 793W H )lob y(CH)17b 888w QO6w y(CH)17. or 10s 922m W H )5

548m 526s 525m-s 510s 672m 674s

508w

mow

277m?

Ref. 1

IR Spectra (cm-')

TABLE 4: Calculated and Experimental' Vibrational Frequencies and Intensities in the Dipolar Form of rn-Aminobenzoic Acid using the AM1 Semiempirical Method.

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

44.6 8.2 58.3

4.2 4.1 4.8 2.3 0.8 100.0 20.2

216.5 39.6 282.9

20.4 20.1 23.1 11.0 3.7 485.6 98.3

85.2 39.7 41.8 158.1 154.4 131.3

1569 1571 1602

1616 1810 1853 1721 I767 2122 3132

3147 3181 3195 3228 3245 3361

100 .Iv,

'y vay bong. 6, -0,

(d. 32)

1557 1599

3004 3018 3051 3062

1.0427 1.0429 1.0427 1.0433

1475

1060 1085 1179 1308 1110 1391

1.lo51 1.lo51

1.0654

1.1051 1.lo51 1.0373 0.9644 12850 1.0451

0.7 0.2

0.7

1.o 1.la 2.6 1.3

11.24 7.68 10.33 1.91 1.70 1.75 16.70 18.21 34.24 624 6.31 6.43 6.52 6.67 6.73 6.81

7.76 5.28 6.83 1.24 1.06 1.oo 9.63 9.90 12.91 1.08 1.08 1.08 1.08 1 1.08 1.02

.w

1.02 0.90 1.25 O.% 1.30 6.71 7.49

1.32 1.11 1.47 1.08 1.33 5.60 6.02

- ,v,

1595m 158Osh 1582vs 1568vs A system of comptex bends in the 3000-2500 an-' range

163611s

-

lS28m

1456m 1492w 1389s

144Ow 1486m 1382vs 1396 vs 1522s 16211637sh

-

1073w 1097w 115Ow 1294111 1223m

1071 vw 111Ovw 1149w 1291 w 1220vw 1308~ v(C=C) 19r + v,(OCO-) v(C=C) 19b v*(OcO-) + v(C=C) 1-

V(NH,') 6(CH) 18. U(CH) 18b b(CH) 9b 6(CH) 3 6(CCC) 1 + V(C-X) 13 v(C=C) 14

m, m m , W, m& w,v e r y w ah,shoulder, br, broad, X, subbtuemt Relatedto h e 38 Calculated vUI,Iym from benzene molecule -1 I v, , v, m from ref 1 v, m from ref 31 Very weak contnbubon of thm mode 'Accordng to nomendaturewed in ref 19

- - - - --

17.5 8.2 8.6 32.1 31.8 27.0

1.8 4.9 8.5 1.2 0.4 0.7 7.1

8.8 23.7 41.4 5.8 2.0 3.2 34.6

1144 1171 1199 1223 1288 1420 1454

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

622

ALCOLEA PALAFOX, GIL, AND NUNEZ

frequencies reported from and some other moleculesL9. Correlations with the infrared bands ofpaminobenzoic acidu and aniline, were also carried out. In Tables 3 and 4, calculated intensities are in M m o l e while the IR relative intensities, given in the fourth columm, are determined by dividing the value of the computed intensity by the intensity of the strongest line obtained (in the study, lines no. 37, 38 in Tables 3 and 4, respectively). The characterization of the bands is shown in the last column. The scale factors (vAMl/veW,) are used to correct the deficiency of AM1 method. The results obtained are shown in the sixth column. Unfortunately, no data are reported for OCO- and NH,’ groups. The theoretical spectrum with these new scaled frequencies is shown in Fig. 3a (dipolar form). The YOerror determined in this way regarding the experimental data is collected in the seventh column of Table 4. The tenth and eleventh columns in this table contain infrared data as published in references 1 and 3 1, respectively. The higher differences between calculated and experimental frequencies are found for OCO and NH,- groups. Comparing the calculated frequencies and the IR data of COOH and OCO- group,it is establishedthat,in the solid state, m-aminobenzoic acid exists in the dipolar form, although with the possibility of a small fraction of molecules in the neutral form. In the NH, and NH,’ vibrations, the calculated Frequencies also seem to confirm the assignation of experimental IR fkq~encies”~’ of the amino group to the protonated form. The ring normal modes, numbered according to Wilson’s are in the characteristic range of m-di-light substituted benzene derivatives3‘.The C-H stretching modes, although not recorded in the IR spectra, due to the overlapping with N-H stretching modes of the NH,’ group, are calculated theoretically by AM 1 in the 3 1Oo-320 cm” range. OTHER MOLECULAR PROPERTIES

In Table 5 are listed the values of the charge and atomic electron density, and in Table 6 are shown several thennodynamic parameters calculated by AM1 in m-aminobemoic acid AM1 method gives a reasonably good description of the stereo-geometry, electron di~tribution’~”~ and ground-state properties compared with MMD0/3 and MNDO methodd9.

623

META-AMINOBENZOIC ACID

0-

I

I

I

I

I

I

I

J f

I 1 VI

> k

.

1

-

v)

W z

f

su.

50-

-1

W IY

loo L-

I

1 ,

I

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

WAVENUMBER

I

I

-

cm"

Fig. 3a. Theoretical spectrum calculated by A M 1 in the dipofur fomi with the scaled frequencies (*).

O i O0

3000

2000

lS00

loo0

500

Wavenumber.cm-'

Fig. 3b. Experimental IR spectrum of rn-aminobenzoic acid in the dipofur form obtained from a Kbr pellet.

In benzoic acid the charge distribution has been reported3' by applymg the SCF-MOmethodwith a value for the carbony1 oxygen atom of -0.582, and values of 0.423 and -0.024 for C7 and CI, respectively, close to our calculations. In the neutral molecule, the great electronegativity of the oxygen atoms gives rise to a partial positive charge on the contiguous carbon atoms, C5 and C7,while the charge is negative in the other carbons.

ALCOLEA PALAFOX, GIL,AND NUREZ

624

TABLE 5: Total Atomic Charge and Electronic Density in m-Arninobenzoic Acid Calculated by the AM1 Semiempirical Method.

-

I anti conformation

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

Atomic Charge

Electronic

Den#

-

I syn conformation Atomic Charge

Electronic Den&

Dipolar fon

Atomic Charge

-0.0787 -0.1903 -0.1554 -0.2428 0.1211 -0.2129 0.3949

4.0644 4.1342 4.0962 4.1881 3.8916 4.1618 3.6497

-0.0786 -0.1875 -0.1568 -0.2429 0.1231 -02188 0.3951

4.0843 4.1321 4.0976 4.1863 3.8898 4.1649 3.6495

-0.1177 -0.1212 -0.1894 -0.1918 -0.2188 -0.1410 0.4567

0.2248 0.1994 0.1952

0.8437 0.8833 0.8665

0.2220 0.1983 0.1951

0.8459 0.8843 0.-

0.2638

-0.5698 02201 -0.3793 02845 -0.3947 0.2928 0.2911

5.4092 0.8471 6.3183 0.7563 6.3042 0.7729 0.7744

-0.5893

5.4085 0.8451 6.3144 0.7563 6.3682 0.7719 0.7744

-0.2171 02575 -0.5284 02983 -0.5615 0.3156 02983

0.2227 -0.3753 02845

0.3988 0.2939 02910

02101 0.1862

-

'wllh trw AMPAC pdooI (nl.23)

In the dipolar form, the negative charge in the OCO-group produces an increase in the negative atomic charge on 0 1 5 and 013, ca. 0.16. This increment in the negative charge on the oxygens corresponds to an increase in the positive charge on the hydrogens and nitrogen of the NH,+ group. The OCO-group withdraws more electrons from the neighbour carbons than the COOH group. Thus, in the carbons of the dipolar form, the lowest net atomic charge (in absolute value) and atomic

Vibrational

Rotelionel

Total Translational

W h the AMPAC peckage (ref. 23).

Entropy (mi Marl K ~:)

Rotationalconstants (G&) :

Heat of formation (kcavMol)' Electronic energy (kcaWol)' lonizabknpdentiel (ev). Dipole moment (Debye)' Zero-pdnt vikational energy (kcellMol) Sum of Thermal e n e m (kCeWl)

Parameter

C

B

A

29.612 20.936

40.658

91206

2.6340 0.9428 0.6943

68.1955 -182750.28 8.5876 3.878 84.5224 89.7597

I anti

-

91.111 40.658 29.809 20.044

2.6951 0.9290 0.6909

68.2598 -182653.38 8.5807 2.974 84.5240 89.7589

I syn

-

20.364

40.658 29.025

96.646

2.5807 0.9481 0.6960

85.5254 91.0743

Dipolar form

Table 6: Some Thermodynamic and Structural Characteristic Parameters of m-Aminobenzoic Acid determined by AM1.

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

el

5

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

626

ALCOLEA PALAFOX. GIL, AND NUNEZ

electron density correspond to C2 and C6, while the highest to C7 atom. A remarkably increase in the electronic density on C5 is also computed, with an increment of 0.34 in the negative charge. Comparing the values with the non-ionized form, an increase of 0.062 in the positive charge on C7 is observed in agreement with a longer C1-C7 bond. In C1 the negative charge is increased 0.039, while in C6 and C2 it is reduced (ca. 0.074 and 0.067,respectively) in accordance with their bonds. Concerning the dipole moment, the available experimental value in the bibliography3' is 2.73 D, in a relatively apolar solvent such as dioxane. This value is close to 2.974 D computed for the syn form, the most stable conformation of the neutral molecule (Table 6). The enthalpies of formation of compounds containing carbon, hydrogen, oxygen and nitrogen by AM1 have been reported to be in agreement with the experimental data" and those obtained by MNDO method, the mean absolute errors being 6.64 (MNDO) and 5.88 kcal mol'

' (AM1).

The zero-point vibrational energies, rotational constants and entropies computed by AM 1 are also shown in Table 6. Close results are obtained between I-anti and I-syn conformations, but lower than in the dipolar form (except in the rotational constant).

CONCLUSIONS The molecular geometry of m-aminobenzoic acid was accurately determined by AM1 theoretical method, the differences being in the standard deviations of this method. The discrepancies in the -COOH group were attributed to the fhct that in the crystal the molecules form hydrogen-bonded dimers O-H-0 through this cahxylic group. In the dipolar form an increase of the C1-C7 (0.072 A) and CS-N1 1 (0.086 A) bonds was computed with respect to the neutral molecule. The agreement between computed frequencies and available experimental data seems reasonable. Us@ scale factors the % error calculated was very small, in the majority of cases less than 4.5 %. In the assignments, most of the relevant vibrational frequencies were in accordance with those repoad in their IR spectra. The vibrations were recognized as characteristic of a m-di-light substituted benzene. Concerning the intensity of the IR bands, in general, the modes not

META-AMINOBENZOICACID

627

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

detected in the spectra were those having the lowest computed intensities. However, the computed relative intensities were not well predicted by AMl, especially in the low frequency range, where the calculated bands were of very low intensity in disagreement with the observed spectra. The AM1 calculation confirmed the dipofar form of maminobenzoic acid in the solid state, although a small fraction of molecules could have been in the neutral form. The values of the total atomic charge, rotational constant and other thermodynamical parameters were also satisfactory. REFERENCES 1.

E. S h c h e z de la Blanca, J.L. N ~ e and z P. Martinez, An. Quim., 82, 490 ( 1986)

2.

(a) A. Thbe Sptmchim. Actu, 274 1 1 (1971). (b) L. Gopd, C.I. Jose and

A.B. Biswas, Specmchim. Actu, 23A,513 (1967).

3.

M. Alcolea, M. Gil and J.L. NGez, Vib. Specmsc., 6, 95 (1993).

4.

(a) A. Harada, M. Hanzawa and J. Saito, Envimn. Toxicol. Chem., 11, 973 (1992). (b) T.W. Schulk, D.T. Lin and L.M. Arnold,Sci. Total Environ., 109110, 569 (1991). (c) H.S. Roscnkmnz, G. Klopman, H. Ohshima and H. Bartsch, Mur. Res., 230,9 (1990).

5.

A. Ludwig, M. Dietel, G.Schaefer, K. Mueller and H. Hilz, Cancer Res.,50,

2470 (1990). 6.

L. Clark, P.S. Shah and J.R Mason,J. Exp. Zoo/., 260,310 (1991).

7.

M.E. Snook, A.S. Csinos and O.T. Chortik, J. Chm. Ecol., 18,1287(1992).

8.

(a) U. Keller and W. Schlumbohm,J. Bbl. chenr,267,11745 (1992). (b) P.S. Miller and C.D. Cushman, Bioconjugafe Chem., 3, 74 (1992). (c) M. Wakdman, J.P. Mazalcymt, J. Xe,J.J. Montagne, A.C. Wain and M.ReboudRavaux, Eur. J. Med.Chem., 26,699 (1991). (d) A. Yamamoto, T. S h e , M.Shibukawa, M. Hashida and H. Sezalri, J. Phurm. Sci., 80,1067 (1991). (e) F. Kasuya, K. Igarishi and M. Fukui, J. Phurmucobw-Dyn., 14,671(1991); 13,432(1990). (f) M. Nagao, M. Nakayasu, H.S h i m S. Aonuma and T. Sugimura, Basic Life Sci., 52,401 (1990).

9.

(a) G. Reinhard, M.Radtke and U. Rammelt,Corros. Sci., 33,307(1992). (b) A.A. AI-Suhybani, Y.H. Sultan and W.A. Hamid, Mureriuhviss. Werksroflech.,

22,301 (1991).

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

628

ALCOLEA PALAFOX, GIL, AND NUREZ

10.

(a) M. Budesinsky, D. Johnels, U. Edlund and 0.Exner, Collecr. Czech. Chem. Comrmm., 56,368 (1991). (b) L.M. Schwartz,RI. Gelb, J. Mumford-Zisk and D.A. LaufeqJ. Chem.Sx.,Perkin T m . , 2,453 (1987). (c) G.C.Levy, A.D. Godwin, J.M. Hewitt and C. Sutcliffe, J. Mu@. Resonance, 29,553 (1978). (d) S. Berger, Tetrahedron,42,2055 (1986).

11.

S.Daishima, Y.Iida and F. Kanda, Org. Mass Specmm., 26,486 (1991).

12.

J.S. Suh and M. Moskovits, J. Am. Chem. Soc., 108,471 1 (1986).

13.

(a) Yu. Ya. Kharitonov and 1.1. Oleinik, DOH.A M . Nark. SSSR, 313, 384 (1990); 2% 151 (1987). (b) S.D.Hamann and M.Linton, Ausr. J. Chem., 29, 1825 (1976).

14.

(a) S.Biihm and J. Kuthan, Collecr. Czech. Chem. Commun.,48, 1019 ( 1983). (b) S. Nhm and J. Kuthan, Inr. J. Quantum Chem., 26,21 (1984).

15. M.J.S. Dewar, E.G. Zoebisch, E.F. Healy and J.J.P. Stewart, J. Am. Chem. Soc., 107,3902 (1985). 16.

M.J. Frisch, M. Hcad-Gordon, G.W.Trucks, J.B. Foresman, H.B.Schlegel, K. Raghavachari, M. Robb, J.S. Binldey, C.Gonraileq D.J. Defrecs, D.J. Fox, R.A. Whiteside, R Sctger, C.F. Melius, J. Baker, R L . Martin, R L . Kahn, J.J.P. Stewart, S. Topiol and J.A. Pople, Gmsim 90, Revision H, Gaussian. Inc., Pittsburgh, PA, 1990.

17.

(a) J.J.P. Stewart,J. Contptrr. Chem., 10,2,221 (1989). (b) W.M.F. Fabian, J. Mol. S m r . (Themhem.), 206, 295 (1990). (c) E. Pop, M.-J. Huang, N. Bodor, S.Bercovici and S. Shatzmiller, J. Mol. Smccr. (7%eochem.),235,343 (1991).

18.

M.B. Coolidge, J.E. Marlin and J.J.P. Stcwart, J. Compuf. Chem., 12, 8, 948 (1991).

19.

M. Alcolea Palafox, J. Mol. S m r . (7’heochem.), 236, 161 (1991).

20.

M.J.S. Dewar and C. Jie, J. Am. Chem. Soc., 109,5893 (1987).

21.

M.Masamura, J. Mol. Smut. (Themhem.), 164,299 (1988).

22.

J.J. Quirante, F. Enriqua and J.M. Hemando, J. Mol. Shucr. (Themhem.), 254, 493 (1992).

23.

D.A. Liotard, E.F. Healy, J.M. Ruiz and M.J.S. Dcwar, in RD. Dmnington I1 and E.F. Healy (Eds.), AMPAC Manual. Version 2.1. A General Molecular

629

META-AMINOBENZOIC ACID

Orbiral Package, University of Texas, Austin, TX,1989. QCPE program no. 506. 24.

J. Voogd, B.H.M. Verzijl and A.J.M. Duiscnberg, Acru Cryst., B36, 2805 (1980).

25.

Y.Xie and J.E. Boggs, J. Compur. Chem., 7,2, 158 (1986).

26. G. Fogarasi and A.G. C*,

Downloaded By: [Palafox, M Alcolea] At: 18:09 15 December 2010

27.

Spectrochim. Acra, 4 4 4 11, 1067 (1988).

(a) D. V. Kumar, V. A. Babu and G. R Rao, Vib. Specfrosc., 4, 39 (1992). (b) D.V.Kumar and G.R. Rao, Vib. Spectrosc., 4,59 (1992). (c) B.V. Reddy and G.R. Rao, Vib. Specmsc., 4,67 (1992).

28. H.F. Hameka, S.L. Emery, G.R. Famini, J.O. Jcnscn, J.M. Leonard and D.J. Ratter, Phosphonrs, Sulficr and Silicon, 53,373 (1990). 29.

H.F. Hmeka, J Mol. S m t . Feochem.), 226,241 (1991).

30.

D. Michalska, L.J. Schaad, P. Ciirsky, B.A. Hess and C.S. Ewig, J. Conrprrr. Chem.,9,5,495 (1988).

31. G. Varshyi, Assignment for VibratioMi Spectm of Seven Hundred Benzene Derivariva, Adam Hilger, London., Vol. 1, pp. 1-30 and 205 (1974). 32.

M. Alcolea Palafox, to bepublished.

33.

B. Lunelli, G. Orlandi, F. Zerbeno and M. G. Giorgini, J. Mol. S a t . Feochern.), 60,307 (1989).

34.

E. Shchez de la Blmca, J. L. NBez and P. Martha, An. Quim., 82, 480 (1986).

35.

E.B. Wilson, Phys. Rev.,45,706 (1934).

36.

M.J.S. Dewarand K.M. Dieter,J. Am. Chem. Soc., 108,8075 (1986).

37.

S.P. Gupta and P. Singh, Indian J. Biochem. Biophys., 14,89 (1977).

38.

A.L. McClellan, Tablesfor Experimental Dipole Moments, W.H. Freeman, San Francisco, p. 247 (1963). Received: November 2,1995 Accepted: December 1, 1995