The dependence of one-bond 13C-13C coupling constants on bond angles - a comment

Tetrahedron Letters,Vol.24,No.l7,pp Printed in Great Britain

1833-1836,1983

THE DEPENDENCE OF ONE-BOND ON BOND ANGLES

Alistair The Dyson

l%-13C COUPLING - A COMMENT

CONSTANTS

G. Swanson

Perrins Laboratory, The University South Parks Road, Oxford, UK.

of Oxford,

The validity of a published relationship between 1J and bond angle is questioned on the grounds that the number CSf couplingpathways contributing to J is not the same for all of the compounds considered.

Abstract:

In early between

0040-4039/83/171833-04$03.00/O 01983 Pergamon Press Ltd.

1982 Mislow

one-bond

in systems

with

has produced constants

carbon-hydrogen a central

a similar

in C-CH2-C

lJcc

The major

and coworkers1

quadratic

systems

= -49.04

difference while

Pomerantz

is that,

coupling,

two different

coupling

CH2 group.

reported

constants

Recent

relating

work

between

electronic

and the CCC bond angle

the systems

and Bittner2

carbon-carbon

coupling

(eqn. 1).

- 0.0056628"

only one pathway

relationship

by Pomerantz

one-bond

to the CCC angle,8

t 1.3378

a quadratic

(eqn. 1) studied

is possible

coupling-paths

by Mislow

and those

for one-bond

are possible

of

C-H

between

adjacent carbons in cyclic molecules and, as Marshall and coworkers have closely to the sum of the shown 3 , the observed coupling constant approximates expected

values

for each pathway

(as obtained

compounds).

The

in alicyclic

molecules

would

contribution

pathway

expected

that pathway

bonds

from the longer to lJCC to be significant only when

from model

is two or at the most

be

three

long

are very

since four-bond coupling constants in non-conjugated molecules 4 small , hence limiting the effect to cyclopropanes and cyclobutanes.

Thus

for 1-methylcyclopropane

and similar

bond

pathways

to the observed

will

contribute

compounds

1 one bond (I-21

1833

both

C(l)-C(2)

one-bond coupling

and twoconstant.

-

1834

An approximate contribution

value

of between

-10 and -15Hz

to JCC in cyclopropanes

observed

carbon-carbon

epoxides

(allowing

coupling

is expected

constants

for substituent

for the two-bond

from

comparison

for cyclopropanes

effects)

of the

with

those

and from the negative

for

values

observed for the central bond of bicyclobutane derivatives 4 . Hence Of Jcc the one-bond contribution to lJ CC in a hydrocarbon with a 60' bond angle would

be expected

constants

to be appreciably

(Table

relationship

Table

than the observed

coupling

in cyclopropanes.

If the cyclopropane Bittner

larger

points

are excluded

1) and the numbers

between

from the data

are replotted

lJ CC and CCC bond angle,8,

1. 15 CC and internuclear

angles.

of Pomerantz

from ref.

,Hz (bond)

8,deg

(eqn.

(angle)

13.3

(l-2)

60 (l-2-3)

l,l-dimethylcyclopropane

12.9

(l-2)

60 (l-2-3)

1,1,3.3-tetramethylcyclobutane

29.8

(l-2)

90 (l-2-3)

1-methylcyclobutane

29.1

(l-2)

90 (l-2-3)

norbornane

30.7

(l-7)

94.4

(l-7-4)

32.5

(l-2)

103.5

(l-2-3) (l-2-3)

bicycle

2.2.2

octane

33.0

(l-2)

109.7

pentane

34.6

(2-3)

112.5

(2-3-4)

l,l-dimethylcyclohexane

33.9

(l-2)

115.0

(l-2-3)

di-tert-butylmethane

35.14

126.5

(2-3-4)

= 14.91

'JCC

The correlation Extrapolation contribution two-bond predicted Since

three-bond

is 0.97 and the standard

of this line to 8=60°

gives an estimated

to JCC in cyclopropanes

of 2&.85Hz,

value

is 0.55Hz.

for the one-bond

and by subtraction

in good agreement

of -11 to -12Hz,

deviation

2)

with

a

Hansen's

value'. similar

contribution improved

(eqn.

+ 0.1660

coefficient

contribution

(2-3)

to

arguments

lJcc

further,

can also be applied

in cyclobutane

although

contributions

derivatives,

at present

the signs

are not known.

to the three-bond this

2).

2)

1-methylcyclopropane

11

and

l), a linear

can be obtained

(data taken

lJcI:

Compound

(Figure

analysis

and magnitudes

can be of such

1835

Figure

while

In conclusion, carbon-hydrogen

coupling

same coupling-pathway one-bond molecules

Mislow's constants

is involved

carbon-carbon

coupling

by the existence

coupling

constant,J.

relationship molecules overall

in which coupling

lJcc

in every

constants

case,

one-bond

since

the

the angle-dependence

of

is complicated

in small-ring involving

it is dangerous

numbers

between

is valid

coupling-pathways

contributions

and bond-angles

different

relationship

these to draw

based

of pathways

can make

conclusions

on data

more

to the observed about

obtained

are contributing

the

from to the

constant.

Acknowledgment studentship.

Hence

between

quadratic

and CCC bond angle

of additional

than one bond and the sizeable

1.

- I would

like

to thank

the S.E.R.C.

for a research

1836

REFERENCES

1. M.W.Baum, 31( 1982)

A.Guenzi,

M.Pomerantz

3.

J.L.Marshall,

Tetrahedron

Lett.,

and S.Bittner, L.G.Faehl

Tetrahedron

and R.Kattner,

Lett.,

%,7(1983).

Org. MaPn.

Resonance,

2,163

.

L+. P.E.Hansen,

Annu.

Rep. NMR Spectr.,

therein. (Received

and K.Mislow,

.

2.

(1979)

C.A.Johnson

in UK 15 February

1983)

=,65(1981)

and references

23,