The long range spin-spin coupling in the carboxylic acid esters

119

NOTES REFERENCES

1. D. W. NAEGELI AND H. B. PALMER, J. &foZ. S~ectry 21, 325 (1966). 2. 1). W. NAEGELI AND H. B. PALMER, “Eleventh Symposium (International) on Combustion, The Combustion Institute, “Pittsburgh.” (to be published). 3. W. J. MILLER AND II. B. PALMER, J. Chen~. Phys. 40, 3701 (1964). on Combustion,” 4. W. J. MILLER AND H. B. PALMER, “Ninth Symposium (International) p. 90. Academic Press, New York, 1963. 5. P. VENIUTESWARLU, Phys. Rev. ‘77, 670 (1950). ARCHIBALD TEWARSON AND HOWARD B. PLAMEX

Department of Fuel Science, Pennsyluania State University, Uniuersity Park, Pennsylvania Received, October Id, 1966

The Long Range

Spin-Spin Coupling Acid Esters

in the Carboxylic

In some aliphatic compounds having no carbon-carbon unsaturation, long range spinspin coupling has been observed between protons which are separated by four or more bonds. Thus in ketones the long range coupling constants were obtained between the protolls attached to the two a-carbon atoms to the carbonyl group (across four bonds) (l-4) ; and in formic acid esters the long range coupling was observed between the formyl proton and the protons which are at the 01. and the &positions to the carboxyl oxygen atom (separated by four and five bonds) (6, 6). Similar long range coupling between protons separated by four bonds was also found in dimethylether, thioethers, sulfones, and sulfoxides (3). In carboxylic the carboxyl between

acid esters other than formic acid esters, the nearest protons separated

group are five bonds from each other, and no long range coupling

these protons.

lines in the NMR protons observed

in carboxylic

state

has been believed

to show two sharp single

the long range coupling

constants

between

these

are very small, bllt are definitely

spectra.

used was a Varian

pure liquid samples

acetate

Now, we have found

acid esters. The coupling

in the steady

The apparatus

Thus methyl

spectrum.

by

was observed

ITS-100 spectrometer

with TMS were degassed

operating

on a vacuum

at 100 Mc/sec.

The

line and sealed in the sample

tubes. The spectra were recorded in the field sweep mode with the sweep rate of 0.02 cps/sec. The coupliug measurements

constants

listed

in Table

and t,he mean deviation

I are average

values

was always within

obtained

from

at least four

rtO.02 cps.

As seen from Fig. 1 both methyl signals of methyl acetate show quartet patterns. *4 spin decoupling experiment shows that the splittiugs of the signals are due to spill-spin coupling with other methyl protons. iso-butyrate

Similarly

give rise to triplet

the methyl protons

and doublet

signals,

of methyl propionate

respectively,

and methyl

as seen from Fig. 2.

The long range coupling constants between the nearest protons separated by the carboxy1 group (across five bonds) in various carboxylic acid esters are summarized in Table I. The order of magnitude of the coupling constants is 0.2 cps, and is considerably smaller than t,he corresponding tion of the coupling srlbstituellts,

values, about 0.5 cps (5), in formic acid ester. Although

constants

with the structural

cannot be deduced

unambiguously

factors,

the correla-

e.g., the electronegativity

of the

from these data, it appears that the pro-

120

NOTES

ton-proton smaller

coupling

than

those

constants

in CHZ-COO-CII,-

in -CH,-COO-CH,

esters. The sign of the coupling

or CHS-COO-CH-

or -CH-COO-CH,

constants,

of course, TABLE

for

are always

the corresponding

is not easily determined,

but we assume,

I

LONG RANGE COUPLING CONSTANTS THROUGH THE CARBOXYL GROUP CARBOXYLIC ACID ESTERS Compounds CH&OOCH3 CH&OOCH&H3 CH&OOCH&H&Ha CH,COOCH(CH& CH$OOCH&H=CHz CH,COO

H,

SOME

J (CPS)

0.21

< H,

‘c=c/ /

Compounds

5 (cps)

IN

H, < Hb N H, <

0.20 0.12 0.1 0.18 0.1 9.9 0.1

CHsCH,COOCH, CH&H&H&OOCH~ (CH&CHCOOCHa CH~=CHCH&OOCHB

0.25 0.19 0.19 0.20

C1CH&OOCH2CH3 BrCH&OOCH&H3

0.19 0.15

\ Hb

CH,COOCH,C,H,

0.13

CNCHCOOCH, ClCH&OOCHz BrCH&OOCH3 Cl&HCOOCH~

0.22 0.22 0.18 0.10

(a)

(b)

CH$l-$COOC~

-

CCH,~CHCOOC~

FIG. 1. Methyl proton signals of methyl acetate. (a) -COO-C& FIG. 2. O-methyl proton signals of (a) methyl propionate

-

and (b) C~3-COO-. and (b) isobutyrate.

121

NOTES

that the sign is the same as that of the vicinal coupling constant in the alkyl chain, i.e., the sign is positive. This inference is based on the double resonance experiments performed on formic acid esters on which we will report in the near future. REFEREKCES 1. H. DREESKAMPUND E. SACKMARTN, Z. Physik. Chw~. (N. F.) 27, 136 (1961). 2. J. R.. HOLMESAND D. KIVELSON, J. Am. Chenl. Sot. 83, 2959 (1961). S. N. VAN ~~EURS, Spectrochi?n. Acta 13, 1695 (1963). 4. K. TAKAHASHI, Bull. Chem. Sot. Japan 37, 963 (1964). 5. D. G. KOWALEWSKI AND V. J. KOWALEWSKI, Mol. Phys. 8,93 (1964). 6. F. HR~SKA, H. M. HUTTON, AXD T. SCHAEFER,Can. J. Chem. 43, 1942 (1965). Government Shibuya-ku, Received

Industrial To~!Jo, Japan

Chemical October

5, 1966

Research Institute,

KIKUKO HAYAMIZU AND OSAMU YAMAMOTO