NH stretching vibrations and conformation of bis[2-(3-substituted ureido)phenyl] disulphides

Journal of Molecular Structure, 197 (1989) 97-104

97

Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

NH STRETCHING VIBRATIONS A N D CONFORMATION OF BIS[2-(3-SUBSTITUTED UREIDO)PHENYL] DISULPHIDES A. TS. ANTONOVA

Faculty of Chemistry, University of Sofia, Sofia 1126 (Bulgaria) (Received 2 August 1988)

ABSTRACT IR spectral data in the uNH region are used to establish the conformation of bis [2- (3-substituted ureido)phenyl]disulphides in some organic solvents. The bis[2-(3-monosubstituted ureido)phenyl] disulphides are in Z/Z conformation forming an intramolecular S ' " HN hydrogen bond and intermolecular N H - " O=C hydrogen bonded associates. The proportion of these associates increases in the order of decreasing solvent polarity (CH2CI2, CHC13, CC14). It is possible that in non-polar CC14 solution these ureas adopt the obviously less polar Z/E conformation. The data obtained support the conclusion that bis [2- (3-disubstituted ureido )phenyl ]disulphides are in the Z form with the NH group taking part in an intramolecular S ' - - H N hydrogen bond.

INTRODUCTION

It has been established that the frequencies of NH stretching vibrations of secondary amides depend considerably on the conformation of the amide grouping. The NH band of the Z form has a higher frequency than that of the E isomer [ 1 ]. These correlations provide a possibility to interpret the conformation of compounds containing the CONH group using IR spectral analysis. The rotational isomerism of various substituted ureas and its dependence on different intra- and intermolecular factors has been extensively studied [2-8]. Definite correlations between conformation and biological activity of some ureas and thioureas have also been found [9 ]. This determines the practical significance of such studies. According to previous spectral studies di- and trisubstituted ureas exist in several conformational isomers on the base of three possible forms: Z, E and non-planar "out" 0

~

c~ N

0 H

H

~N ~ R

Z

0022-2860/89/$03.50

0

II

C

~

R

II ,,~bN C H

E

out

© 1989 Elsevier Science Publishers B.V.

98 The presence of different isomers depends on various factors such as the kind of substituents at the ureido grouping, the medium, etc. It was observed that in the vNH region of IR spectra of bis [2- (3-substituted ureido)phenyl ]sulphides 1 and 2 there were some characteristic features: in comparison with other disubstituted ureas investigated in solution [2, 3 ] the associated pNH band of ureas 1 has much higher intensity than the monomeric band at all concentrations studied; the trisubstituted ureas 2 have only one sharp band in the interval 3400-3383 c m - 1 In this connection in the present paper N H stretching vibrations are used to establish the conformation of the ureido groupings of compounds 1 and 2 synthesized by aminolysis of 2 (3H) benzothiazolone using primary or secondary amines [ 10, 11 ].

NHcoHN CrNHc°NN S

S

S

S

RNH2 ~N.~ H O--

RRNH

RRNCOHN-~ [~NHCONRR 2

EXPERIMENTAL The model ureas 3, 4 and 5 were obtained by interaction of the corresponding amine and isocyanate [ 12-14 ]. The IR spectra were recorded on a Perkin Elmer 983G grating spectrometer (the wavenumbers are accurate to + 1 cm -1) and a Carl Zeiss UR-10 spectrometer. The integrated intensities were determined using the standard software provided with the Perkin Elmer 3600 data station. NaC1 cells were used. RESULTS AND DISCUSSION Ureas 1 have two bands with greatly differing intensities in the gNH region in CHC13 solution: a sharp band at 3441-3431 cm -1 (band A) and a second, broader and considerably more intense band at 3363-3355 cm -1 (band B). Table 1 and Fig. lb show that the intensity of band B is about 85% of the total intensity of both. The shape of the spectra at different concentrations is almost identical, i.e. the intensity of band B is higher than that of band A and the ratio of intensities IB/IA increases with the concentration {Table 2 and Fig. 2). At increased con-

99 TABLE 1 ~NH Wavenumbers and intensities of ureas 1 in CHC13 (2.5x10 -2 M)

IB/IA

Compound

A band

No. R

Wavenumber I " (cm -~) (kin mol 1)

(%)

Wavenumber I (cm-') (km tool -1)

(%)

la lb lc ld le

3441 3441 3445 3439 3431

14 14 15 16 17

3361 3362 3363 3359 3355

86 86 85 84 83

n-C3-H7 n-C4H9 i-C4H9 C6HsCH2 C~H~I

B band

85 86 87 115 92

543 550 505 600 451

6.4 6.4 5.7 5.2 4.9

"The intensities of A and B band are estimated by assuming that both have the same absorption coefficient. lO0' ,x

/

1

8C

V

60

i

tr)

V

a

c~

I

i

t~

~

o

c~

b

c

i

i

t~

i

i

o~

Fig. 1. Solvent effect on vNH bands of urea l b (conc. 1.0×10 -2 mol dm -3, 1 mm cell): (a) in CH2C12; (b) in CHC13; (c) in CCI4. TABLE2 uNH Wavenumber (cm -1) of urea l b at different concentrations in CHCI:~ Concentration (M)

A band

B band

4.2×10 -'~ 1.0×10 -2 2.5 × 10- 2 1.5×10 -1

3443 3441 3441 3441

3365 3366 3362 3334

centration the two bands preserve their positions, except band B at the highest c o n c e n t r a t i o n s t u d i e d , w h i c h s h i f t s t o 3334 c m - ' . T h e s e r e s u l t s p r o v e t h e form a t i o n of i n t e r m o l e c u l a r h y d r o g e n b o n d s .

100 1oo

~oc

i

86-

ao.

~ ~" 2 E k

60-

i

i i

cm

- t

Fig. 2. vNH Bands of urea l b in CHCI3: (a) conc. 1.5×10 -1 mol dm -3, 0.1 mm cell; (b) conc., 4.2 × 10 -3 mol dm -3, 1 mm cell. TABLE3 vNH Wavenumbers and intensities of ureas 3 in CHC13 (2.9 × 10- ~ M) Compound A' band No. Wavenumber I (cm -1 ) (km mo1-1 ) 3a 3b

3434 3429

150 90

B' band

I~./I A

(%)

Wavenumber I (cm - I ) (km mo1-1 )

(%)

49.6 39

3362 3351

50.4 61

152 140

1.01 1.6

There are also two N H stretching bands (A' and B' ) in CHC13 solution in the spectra of 1-n-butyl-3-phenylurea ( 3 a ) and 1-cyclohexyl-3-phenylurea ( 3 b ) , which are close structural analogues of ureas l b and l e . These bands are situated almost at the same positions as the corresponding A and B bands of ureas 1. However, Tables 1, 3 and Fig. 3 show that the intensity ratio IB,/IA, of ureas 3 is several times lower than that of ureas 1 at the same concentration. The comparison with the N H stretching bands of ureas 3 and also with those of a large number of 1,3-disubstituted ureas [2, 3, 5] reveals that the presence of a disulphide group in ureas 1 results in much higher intensity of band B.

101

100

:1

80 I.-...

60 I

I

~ c m -¢ ub r,)

Fig. 3. ~NH Bands of urea 3 a in CHC13 (cone. 2.9X

10 - 2

mol dm -a, 0.6 mm cell).

I.....

20 c~

~

~

k~

.4. ~'~

~'~ ~'~

e m "~

Fig. 4. vNH Bands of urea l b in CC14 (cone. 3.0× 10 -4 mol dm -a, 50 mm quartz cell).

Definite evidence for the presence of an intramolecular S - - - H N hydrogen bond in ureas 1 is obtained from the spectrum of urea l b registered in dilute CC14 solution (cone. 3.0 × 10 -4 mol dm -~) using a quartz cell. As can be seen in Fig. 4 there are two bands in the v N H region of this spectrum: a monomeric band A at 3445 c m - 1 and a more intense band B with a maximum at 3375 c m - 1 and a shoulder at 3350 c m - 1. It follows that band B is formed by two overlapping bands: the first at 3375 cm -1 corresponds to N H stretching vibrations taking part in an intramolecular S - " H N hydrogen bond [ 15, 16 ] and the second (the shoulder at 3350 cm -1) corresponds to N H groups involved in an intermolecular N H . " O=C hydrogen bond. The position and intensity of the second band depend strongly on the concentration. Table 4 and Fig. lc show that in a more concentrated solution (1.0× 10 -2 mol dm -3) the monomeric band A decreases its intensity to about 5% of the total intensity of A and B bands. The intensity of the association band increases rapidly with concentration and eventually overlaps entirely the band due to the intramolecular S--" H N hydrogen bond at 3375 cm-1. All results and comparisons reported up to this point lead to the conclusion

102

TABLE 4 ~NH Wavenumbers and intensities of urea l b in different solvents (1.0 X 10-2 M) Solvent

A band

CH2C12 CHCla CCI4

B band

Wavenumber (cm- 1)

I (km mol- i )

(%)

Wavenumber I (cm- 1) (km mol- 1)

( %)

3436 3441 3445

126 87 46

19 15 5

3363 3362 3337

81 85 95

549 505 951

that in CHC13 solution ureas 1 are in Z/Z conformation I. The high frequency band corresponds to a monomeric N H group bond to the alkyl substituent, i.e. to the N H group whose frequency is near to that (3447 cm -1) of the model 1,1-diphenyl-3-n-butylurea (4). The low frequency and more intense band B is due to the stretching vibrations of the N H groups taking part in intermolecular N H - ' . O=C and intramolecular S ' . . H N interactions.

II \ /

C~O-..H

I

t..

..

H"

z/z

I

" H

/

H" "'O~C

\

I

The data given in Table 4 and Fig. I clearly show that in order of decreasing polarity of the solvent (CH2C12, CHC13, CCI4) the intensity ratio of band B to band A increases, which is in accord with the well known fact that the formation of associates is favoured in non-polar solvents. It is also possible for ureas 1 to adopt the obviously less dipolar Z/E conformation (II) in non-polar solvents, preserving the intramolecular S " - H N hydrogen bond. There are no concrete data, however, that such a rotamer is present in the compounds studied. o

O

II

II

~ ~ N / C . . . N ~H"" I

~

\ c~o /

H ~N/'C~N/R

. . . HL ~ ' s

Z/E

H"• •O ~ C

II

Ureas 2, synthesized by aminolysis of 2 (3H) -benzothiazolone with secondary amines, have only one sharp N H stretching band at 3400-3383 cm -1 (Table 5 ) whose position does not depend on the concentration (up to 1.0 X 10-1

103 TABLE 5 vNH Wavenumbersof ureas 2 in CHC13 (1.5X 10-2 M) Compound

Wavenumber (em-1)

No.

RR N

2a

/--1 Nk~]

2b

N

2c

N (C2H5)2

o

Wavenumber (era-1)

Compound No.

RR N

3383

2d

N{n-C~HT)2

3398

3391

2e

N (n-C4Hg)2

3400

3398

2f

w~

3400

tool d m - 3 ) and the medium (CHC13, CC14). Its frequency is decreased by only about 15 cm-1 in the solid state (nujol). This band is situated at 63-80 c m - ' lower wavenumber t h a n the N H stretching band (3463 c m - 1, Z isomer) of the model 1,1-pentamethylene-3-phenylurea (5). The results obtained show t h a t ureas 2 exist in Z conformation III. The N H group is involved in an intramolecular S ' " H N hydrogen bond observed in a similar frequency interval as in their analogues 1.

! Z

III

The absence of an association band in ureas 2 agrees with the conclusion of Mido and Furusawa who do not observe the formation of associates in the trisubstituted ureas when an intramolecular hydrogen bond exists [4]. ACKNOWLEDGEMENTS The author t h a n k s Mr. T. Dudev and Ms. M. Ilieva for recording the spectra and Drs. M. Arnaudov and B. Galabov for helpful discussions.

REFERENCES 1 2 3 4 5

H.E. Hallam and C. M. Jones, J. Mol. Struct., 5 (1970) 1. Y. Mido, Spectrochim. Acta, Part A, 29 (1973) 431. Y. Mido, Spectrochim. Acta, Part A, 29 (1973) 1. Y. Mido and C. Furusawa,J. Mol. Struct., 82 (1982) 23. Y. Mido and T. Okuno, J. Mol. Struct., 82 (1982) 29.

104 6 7 8 9 10 11 12 13 14 15 16

Y. Mido, H. Okada and T. Iton, J. Mol. Struct., 65 (1980) 35. Y. Mido and T. Gohda, Bull. Chem. Soc. Jpn., 48 (1975) 2704. B. Galabov, V. Kalcheva and B. Hadjieva, J. Mol. Struct., 158 (1987) 259. A. Galabov, B. Galabov and N. Neykova, J. Med. Chem., 23 (1980) 1048. D. Simov and A. Antonova, C. R. Acad. Bulg. Sci., 21 (1968) 881. A. Antonova and D. Simov, Annu. Univ. Sofia, 80 {1986) in press. T.L. Davis and N. D. Constan, J. Am. Chem. Soc., 58 (1936) 1800. A. Skita and H. Rolfes, Bet., 53 {1920) 1242. N. Gebhardt, Ber., 17 (1884) 3033. J. Scribner and J. A. Miller, J. Org. Chem., 32 (1967) 2348. P.I. Krueger, Tetrahedron, 26 (1970) 4753.