Infrared studies with terpenoid compounds—VI

Tmclhrciion. Vol.25.pp.36171oM22.

Rrgamon~1969.

INFRARED INFRARED

SPECTRA

RintediaGratBriti

STUDIES WITH TERPENOID COMPOUNDS-VI’ OF PENICILLIC

ACID AND ITS DERIVATIVES

S. KOVACand E. ~OLCANIOVA Institute of Organic Chemistry, Slovak Technical University, Bratislava, Czechoslovakia and

G. EGLINTON Chemistry Department, Glasgow University, Glasgow, Scotland (Received in the UK 14March I%9 ; Accepted for publication 1i’ April 1969) Abstract-An abnormally persistent self-association of penicillic acid in solution has been observed. With alI compounds studied an unusually high molar absorptivity of (v& is reported.

self-association has been observed with some substituted steroids. An explanation for this type of association based on the nature and stereochemistry of the interacting groups has been reported.‘, 3 In the present work we report another example of an unusually strong selfassociation, observed with penicillic acid, and also abnormally strong absorptions (v& with penicillic acid (I), penicillic acid acetate (II) and methyl penicillate (III), respectively. UNUSUALLY

strong

phenols and di and trihydroxy

RESULTS

AND

DISCUSSION

From IR spectral data (Table 1) it follows that penicillic acid (I) strongly selfassociates as the two concentration-dependent bands in the OH and CO regions, are observed at the relatively very low concentration in carbon tetrachloride (08 mM). The stretching absorptions of OH (free) are shifted upwards with a change from carbon tetrachloride to chloroform as solvent (3590 + 3574 cm- ‘) while the OH (bonded) shifts in the opposite direction (3300 -+ 3342 cm- ‘) which is in accord with the spectral data of OH absorptions. If an approximation of the position of band centre of OH (bonded) is made, then it is found that it is less inlluenced by solvent than it would seem from a simple inspection. Progressive dilution of I in carbon tetrachloride reveals a further band at 3548 cm-’ which almost certainly represents the first overtone of the fundamental (v-). In the carbonyl region (I) a small shift for (v-) bonded to higher frequencies (1746 --* 1752 cm- ‘) upon dilution from 16 to 08 mM in carbon tetrachloride solution has been observed. Examination of the Dreiding model (Fig. 1) of penicillic acid shows that there is no steric hindrance for the intermolecular H-bonding of the cyclic “dimer” type. Both interacting OH and CO groups in the two molecules of this compound can l

Present address: The Chemistry Department, Bristol University. England. 3617

051 1.0 2.0 2.0 5Q 5.0

80 500 25.0 12.5 6.25 3.125

CCb

d Shoulder at 1.728 cn- r.

v and Avt, am in cm-r;

CHCls

20 5Q 20.0 2OQ 20.0

-

(mtt

cell

42 41 40 41 41 42

26 26 25 25 25 75 85 95 100 110 125

V

3,342 3,342 3,342 (3,342) (3,342) -

260 255 -

228 226 230 230 40 30 20 (15) (15)

100 80 45 30 (15)

s,

AHSOIIPTIOSS

Bonded Av,,

3Jw 3,302 3,320 (3,345) (3,345)

vOH

SIWLI(‘HI\G

35 50 85 loo 120

so

(‘

011 011 011 011 0.51 1.0

05 05 2a 50 5.0

paths (mm)

Cell

1,768’ 1,767’ 1,767 1,766 1,767 1,767

1,777 1,778 1,777 1,777 1,779

v

OF PtNl~‘II.LK

I,

640 670 725 735 735 735

195 250 465 520 675

E.

v 24 (28) (28) -

Bonded Avt,

530 480 360 220 (75)

q,

TEIWAC HLOKIIN

1,746’ 1,746’ 1,747 1,752 1,752

VCO

<‘ARHoN

1,645 1,644 1,644 1,644 1,645 1,644

(13) 13 13 13 13 13

17 17 17 17 16 -_

vC==C Av*

1,080 1,Ow 1,090 1,090 1,080 1,090

850 850 860 860 870

a,

( III OROtOHI~

1,641 1,642 1,643 1,645 1,646

v

Ahl)

1; b A symmetrical band ; ’ Shoulder at 1730 cm- ’ ;

33 31 27 25 26 25

(23) (23) 22 20

Free Av+

AC’,,,

Values in parenthesis are approximate; ’ Band at 3,548 cm-

3,574 3,574 3,574 3,573 3,574 3,573

C‘

Free Av h*

I A\I)

3,58Y 3,589’ 3,5W 3,591’ 3,592

v

I.. ( .\RIIO\\

16 8 3.2 1.6 D8

Cone

I. HI I)KO\~

(mm

k

s”‘vent

T.\NI

Infrared studies with terpenoid

compounds--VI

3619

approach within bonding distance -YEA. The combined IR (Table 1) and osmometric data (Fig. 2) for apparent molecular weights in carbon tetrachloride solution suggest that the associated species is mainly “dimer”.

FIG. 1 Planar projection of the Dreiding molecular model of the “dimer” of penicillic acid. The dotted lines indicate the hydrogen bonds.

FIG. 2 Plot of the ratio W/%4 of the apparent (W) to true (M) molecular weight against molar concentrations in carbon tetrachloride: A-penicillic acid and o-stearic acid.

The abnormally strong self-association of penicillic acid (I) in solution may be due to the presence of the bulky substituents of (CH,) WH,, bonded to the same C atom as the OH groups, which hinder the H-bonds against the molecules of the solvent. Osmometric studies (Fig. 1) also indicate that penicillic acid (pKi&, 590)4 selfassociates more strongly than does ethyl coumarate,’ which is roughly equivalent to stearic acid (pKz&o 590).5 The self-association of penicillic acid in chloroform is weaker than in carbon tetrachloride solution (Table 1). The stretching absorptions being shifted by 5 cm- ’ upwards upon of vc=T (I) are also concentration-dependent, dilution in carbon tetrachloride. This could be attributed to OH . . .1c bonding. The UV spectrum of penicillic acid displays only one concetrationdependent band. In cyclohexane (Table 3), the band decreases in wave-lengths as the concentration is increased (A,,, 226221 mu) while the intensity is increased (8,837O + 10,830 1.mole- 1 cm- ‘) over the range of concentrations from 0394 to 0785 mM. In ethanol solution, there is a significant decrease in intensity of the band (c“. 6800 I. mole-’ cn- ‘) at concentrations approx equal to those’used in cyclohexane (Table 2). c+Unsaturated-y-lactones bearing and rx-hydrogen almost invariably exhibit CO absorptions of complex shape and Fermi resonance involving the CO stretching

CCL

CCL

Cyclohexane

SOhXlt

241

11.97 ~~ 230

Cone

-

13

v

Vo,(-OAc)

1.803’

1,806

(mM)

(650)

1,080

Av,

13

V

Vw(FC02W

1.718

E,

710

Av,

1,687

15

-

(15)

Avr

Vco(>w

1,777 1,776”

v

500

810

670

E.

V

1,618

1,651

1,652

PENICILLICACIDACETATB(TI)AM)~LPEMCILLATE(III)

13

14

720

1,015

Av+ E, -.__-13 925

VC=C

Cell paths 05 mm; Values in parenthesis are approximate; v and Avt, are in cm-’ ; - not measured; ’ Very broad band Avt, _ 43 cm-’ and the third maximum is at _ 1,785 cm- ‘.

III

II

Compound

TABLE ~.CARBONYLAND~~CHINGABSORPTIONSOF

3621

Infrared studies with terpenoid compounds-VI TABLE3. UV A-

ON SPECTRAL

DATA

R3R

PENICILLIC

MErHYLPENlClLLATe

Compound No.

solvent

Cone mM

229

(I),

P@NlClLLlC

226

L(w) 224

ACETAlE

(II)

AND

223

221

9230

0157b

10,830

OQ78Sb

I

ACID

(IID

8,370

0394’ cyclohexane

ACID

E ethanol

Q294’

II

ethanol

O-236’

III

ethanol

6,800

10,600

0271’

19500

00271’

20,600

cell paths(in mm): o 5-O; ’ 10-O; c la.

frequency. The first overtone of the y(CH) of the u-hydrogen has been postulated by Jones et ~1.~ The relative intensities of the observed pairs of bands of the y-lactones reported previously’* ’ are strongly solvent-dependent and the frequencies show much smaller and more irregular shifts than normal CO groups which is in accord with the literature findings. Penicillic acid (I) as a a&unsaturated y-lactone is an exception as this compound exhibits only one band in the CO region at extremely low concentration in carbon tetrachloride solution (Table 1). However, some splitting (shoulder at 1730 cm- ‘) and a small increase in intensity of the v(W) band in chloroform solution is observed (Table 1). This spectral anomaly, may be explained by isotopic substitution or by the investigation of more a&unsaturated y-lactones. All compounds studied exhibit very strong bands assigned to the absorptions of the C=C bond (I), k 860; II, E” 1015 and (III), d, 720 1.mole-’ cm-’ in carbon tetrachloride (Table 1 and 2). In a large number of non-conjugated compounds the C=C stretching vibration gives rise only to weak bands in the IR. In many cases the main factors influencing both the frequency and the intensity are symmetry considerations, conjugation and the nature of substituents on the two C atoms bonded by a double bond.’ Especially, the alkoxy substituents greatly intensify C=C bands as reported for vinyl ethers,‘O cyclopent-2enones and cyclohex-2-enones, l1 and phorone derivatives. ’ 2 Electronrelease (+ M) by the OMe group could be the main factor in determining the C=C intensity in the compounds studied, but the problem requires further study on systems similar to those of penicillic acid and related compounds.

3622

S.Kov&E.

SOLCAN~OVA~~~

G.EGLINTON

EXPERIMENTAL IR spectra were recorded with a Unicam S.P. 100 double beam spectrophotometer equiped with an S.P. 130 Naa prism-grating double monochromator operated the general procedure described prcviously*.Thc apparent half-band widths, A#, arc quoted to the nearest integer; where necessary they were determined by reflection of the undisturbed wings of the unsymmetrical bands. Intensities are given as apparent molar absorptivitits, E’,(I. mole-’ cm- ‘) rounded to the nearest 5 units. UV spectra were recorded with a Unicam S.P. 800 double beam spectrophotometer over a range of concentrations of @8 to 17 mM in cyclohexane. The mol wt measurements were carried out with a Mmhrolab, model 301 A vapour pressure osmometer over a wide range of concentrations in CCl,. Muteri&. Analar CHCl, and cyclohexane (spectroscopic grade) were used without further purification. Analar CHCI, was dried several times by passage through a column of blue silica gel before use. The purity of compounds examined was checked by IR spectroscopy and gas chromatography. Acknowledgement-We thank the British Council for the award (to S.K.) of a fellowship. We also thank Mrs. F. Lawrie for assistance with some of the measurements and Professor R. A. Raphael and Dr. B. Caddy, both of Glasgow University, for generously supplying samples.

REFERENCES

1 Part V: S. Kovac and G. Eglington, Tetrahedron 25,3259 (1969). 2 3 4 ’ 6 ’ s ’ lo ” I2

W. S Bennet, G. Eglinton and S Kovac, Nature 214, 776 (1967). S. Kovac and G. Eglinton. Tetrahedron. 25. 3259 (1969). J. E. Page and F. A. Robertson, J. Chem. Sot. 133 (1943). N. P. Fatta, J. Ind. Chem. Sot. 16,573 (1939). R. N. Jones, C. L. Angel], T. Ito and R. J. D. Smith, Canud. J. C&m. 37,2007 (1959). R. P. M. Bond, T. Cairns, J. D. Connoly, G. Eglinton and K. H. Overton, .I. C&m. Sot. 3958 (1965). T. Cairns, G. Eglinton, A. I. Scott and D. W. Young, Ibid. 654 (1966). L. J. Bellamy, The Infrared Spectra ofComplexMolecules (4th Edition) p. 62 Methuen, London (1964). R. H. Hall, A. R. Philpotts, E. S. Stem and W. Thain; J. Chem. Sot. 3341 (1951). H. N. A. Al-Jallow and E. S. Waight, Ibid. (B) 73 (1966). H. N. A. Al-Jallow and E. S. Waight, Ibid. (B) 75 (1966).