The NMR spectra of basic primary alcohols

Tetrahedron Letters No.24, pp. 1941-1942, 1969.

Pergamon Press.

Printed in Great Britain.

THE NMI? SPECTRA OF BASIC PRIMARY ALCOHOLS R. J. Bass and 8. J. &well Research Division, Pfizer Limited, Sandwich, Kent. (Received in UT 8 April 1969;

accepted for publication 24 April 1969)

It is luxwn that many alcohols may be classified by observing their spectra in dimethylsulphoxide

(DMSO) (11.

In the latter strong hydrogen bonding to the solvent shifts the

hydroxyl resonance downfield and reduces the rate of proton exchange so that spin-spin coupling of the hydroxyl proton may be observed.

This situation

(21 does not always hold however, as the

method has been found unreliable for a number of alcohols having strong electron-withdrawing substituents close to the hydroxyl group.

It is concluded (21 that structure and perhaps geometry

ore important as well as electronegativity. The absence of the expected spin-spin coupling between the hydroxyl and methylene nrotons of o-aminobenaylalcohol

in DMSO prompted us to look into the problem further.

apparent that the amino group of.+aminobenzylalcohol

It is

is sufficiently basic to accelerate the

hydroxyl proton exchange rate so that loss of multiplicity of both hydroxyl and methylene resonances occ"rs. The NMB spectra of a number of alcohols containing basic centres and of benzyl alcohol in the presence of equimolar quantities of bases of varying pKa have been examined.

The

results are shown in the following Table. No.

Alcohola

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

Benzyl alcohol Benayl alcohol Bensyl alcohol Bensyl alcohol Benzyl alcohol o-Nitrobenzylalcohol o-Aminobensylalcohol 3-Hydroxymethylpyridine 5-8-Hydrolry-4-methylthiazole Y-Dimethylaminopropanol 3-Hydroxymethylpyridinium methiodide 3-Hydroxymethylpyridinium methiodide 3-Hydroxymethylpyridinium methiodide o=N,N-dimethylaminobenzy~ alcohol L(o-Hydroxymethyl)pheny~trimethyl ammonium iodide

Added Base

pKab

o-nitroaniline m-nitroaniline phthalazine aniline

-0.28 2.45 3.47 4.62

o-nitroaniline pyridine

-0.28 5.23

1941

Spin-spin coupling -CH20H Yes Yes Yes partialC No Yes No No NO NO Yes Yes No No Yes

1942

No.24

Footnotes

to Table *All spectra Varian b

Taken

A60

were

obtained

intended

benzyl

coupling alcohol

without

coupling

was

of the hydroxyl

just discernable Entries

coupling

occurs

with

by Albert

for aqueous

and

solutions

of the absolute

bases

broadening.

centre

has been removed

benayl

alcohol

by quaternisation.

and its corresponding

limiting

to benzyl was

added

of the respective

and meta-

case

is added

When aniline

broadening

such as ortho-

appeared

nitroanilines,

to

multiple& coupling

to bt? phthalazine

where

resonancea.

are alcohols

of the hydroxyl,

3-hydroxymethylpyridine

aniline

is removed.

a gradual

The

on the broadened

exchange

equimolar

protons

equivalent,

7 to 10 in the Table

proton

that when

and methylene

of weaker

any noticeable

rapid

are those

from the Table

On the addition

occurred

values

Constants

to be an indication

in less than a molar

was observed.

to facilitate

on Ionisation

in DMSO solutions.

It can be see" alcohol

on a

.

These

(1962).

and are not basicity

in DMSO solutions

instrument.

from the manual

Serjeant

as 10% "/v

thus causing

in contrast A similar

methiodide,

containing

with

a sufficiently

loss of multiplicity.

its methiodide

situation

basic

exists

with

in which

centre No

the basic

o-N,N-dimethylamino-

LT o-hydroxymethyl)phenyl/trimethyl

ammonium

iodide. It can be see" alcohols

must

be taken

from this

into account

when

limited

study

interpreting

that the presence their

spectra

of basic

centres

in L)MSO solutions.

References 1.

0. L. Chapman

2.

J. G. Traynham

and R. W. King, and G. A. tinesel,

J. Amer. ibid.,

Chem. 8&

Sot., X 86, 1256 4220

(1965).

(1964).

in