Transposition of linear alkyl-chains into ramificated chains.

International Journal of Mass Spectrometry Elsevier

Scientific

TRANSPOSITION

(France)

Company,

OF LINEAR

H. E. AUDIER Laboratoire

Publishing

47 (1983)

and Ion Physics,

Amsterdam

ALKYL-CHAINS

-

Printed

INTO

475

475-478

in The Netherlands

RAMIFICATED

CHAINS

.

and A. MILLIET de Synthese

Drganique,

Ecole

Polytechnique

PALAISEAIJ

91128

Cedex

.

ABSTRACT It is shown by the study of alkyl ethers and benzoates , that formation of ions is preceded by an isomerisation of the alkyl-chains leading to a substituted ethylenic ion . A mechanism of isomerisation is proposed for the respective intensities of peaks and the values of appearance'energies in the spectra of labelled compounds . The fragmentation is initiated by the shift of one H at pos7tion 3 leading to an intermediary complex in which a neutral molecule interacts with a [CnHZnl+ ion .

[CnHznl+

INTRODUCTION The ether ion

similarity (ref.1)

(ref.2) The

which

of the MIKE

and the great

leads

to the suggestion

intermediate can

- break,

complex

be schematized

- isomerize

and give

leading

spectra

n-butyl

of the peak

of an alcohol

as a methylcyclopropane,

IM-C2H51+

- as shown

and

shown molecule

can

ethyl-isobutyl to the

scheme

IM-C2H51+

1 (ref.1)

.

and a [C4H81+ ion,

:

ion

by the A.E.

value

___2’.‘*

H

C&OH

ether

corresponding

of the mechanism

composed

/-y-J +

of ethyl

intensity

- to a disubstituted

ethylenic

z t

-I

-&---A

f

3

Scheme

C2H5

1

ETHYL-PENTYL-ETHERS The

study

risation

of ethyl-pentyl-ethers

: the intensity

of

0020-7331/83/0000-0000/$03.00

corroborates

[M-C2H50HJf 0

peaks

the proposed of MIKE

1983 Elsevier Scientific

spectra

mechanism is much

Publishingcompany

of isomegreater

476 tha-n those

of

inferior

'stable methyl-2 chain

.

TABLE

1 -

ALKYL

homologues

buten

Ratio

ion is formed

of intensities

: there

show that

is once

IM-C2H50Hl+hain

more

a transposition

of the

peak

ethyl

n-propyl

0

s-propyl

0

n-butyl

5

s-butyl

0

ethyl

n-pentyl

90

a particularly.

s-pcntyl

i-butyl

12

7

i-pefltyl MKl

BENZOATES

B CC5H5C(OH)21

structure i) only l-buten, to that ii) when ethylenic very

of

values

ethyl

The 70 eV spectra and

. . The.A.E.

(table

peaks

the transfer

intense

essentially

the AJB ratio

A IM-C5H5COOH1+

depends

on the chain

2-butyl

2-hexyl

. The AHf of final

and 3-methyl

[A) c A-E.

WI+

[BI+

Cd

0

s-but

0

n-pent I

0

.Table

benzoates)

the two peaks with

R

E

--G

i-but

have

a

of B is inferior

the A .peak is

AHf of final

2

+

states.

have comparable

trisubstituted

2

1

R

state

corresponding

compatible

Scheme

n-but

A ion should

lead to a trisubstituted

2-pentyl

benzoates

of A is only

[Al+

0 can

(B) a's the

and 3-hexyl

value

for which

(B)

of a BH on the carbonyl

. Then A.E.

the A.E.

of benzoates

structure

(A) > A.E.

(3-methyl

iii) for 2-pentyl intensities,

on spectra

or isobuten

of A, and A-E.

ion

exhibit

. On MIKE spectra

2) .

B ion is present 2-buten

of alkyl-benzoates

0,60

ethyle-

477

when

a spectrum

negligible

[M-C6H5COOH]+

70 eV or

conclusions

- the similarity n-butyl

which

(scheme

3)

the

BH shift

states

are rather

of n-butyl: benzoate

is not

yH shift

high

is

(ion A

is slow

.

: of isobutyl

and n-butyl

benzoates

(comparison

1)

of the spectra

benzoate

spectrum

explain scheme

final

fragmentation

of the spectra

the ethers,

12 eV energie.

15 X), but on MIKE spectra,

36 % and

[M-H,O]+),

and

- the similarity with

taken with

. As AHf of the more stable

selective

These

js

(respectively

of the

are very

l,l-d2n-butyl

different

from

benzoate

3,3-d2n-butyl

and the 2,2-d2 benzoate

.

Scheme

3

CONCLUSION The same

- during

type of mechanisms

the fragmentation

a cyclopropanelike - the fragmentation (ref.4)

(scheme

form

have

of methyl-2 is observed

of halogenated 4)

been proposed propen

in the

an exchange

literature of carbon

: through

(ref.3)

phenoxyde

is preceded

_

Scheme

4

by a carbon

permutation

478 Several being MIKE

other

The MIKE

of isoamylamine spectrum

On the spectrum 50 % of this

showing

. For instance

studied spectrum

examples

the

the general presence

proceeds

of phenyloxetan

of the 3.3-d*

ion remains

of an intense

via this presents

phenyloxetan

at m/z

character

of this mechanism peak

an important

104 and the residue

5

2 3 4

H.E. Audier, G. Bouchoux, Y. Hoppilliard and A. Milliet 1982, to be published . Org. Mass Spectrom., C.E. Hudson and D. J. McAdoo Org. Mass Spectrom., 14, 109 (1979) . M.S.H. Lin and A. Harxson Can. J. Chem., 52, 1813 (1974) . C.B. Theissling7N.M.M. Nibbering and Th. J. de Boer Adv. Mass Spectrom., 5, 642 (1971) .

(scheme

ion

(m/z

phenyloxetan, at m/z

R=D,R=H

REFERENCES 1

styren

is found

R=H Scheme

58 on the

type of intermediate

as of the 4,4-d2

R=D

at m/z

are

106

5) .

104) about

.

m/z

58

.