Citric acid mass spectrum

[bunnahabhain]

Dear all

I have recorded a mass spectrum of citric acid, and I found three masses:
191 = [M-H]-
173 = [M-H2O-H]-
111 = ???

What is 111? It is not an artifact, see
http://www.massbank.jp/jsp/FwdRecord.jsp?id=PR100481

Any idea ?
Thanks a lot,
Jörg

[JMB]

Surely it is the loss of O=C(OH)2 from m/z 173.

Regards,

JMB

[bunnahabhain]

Thanks JMB

The masses match, but I can't imagine how such a structure might be formed (lack of fantasy?).

Jörg

[JMB]

Jorg,
Well I don't have the skills to draw the mechanism here, but I think that it is a 4-centre one.

C1 is -C(O)OH

C2 is >CH2 linked to C1

C3 is >C=CH(O)OH

C4 is -C(O)OH linked to >C=C(O)OH

and the product ion is CH2---C=CHC(O)O-
cyclopropyl
C=O
which has 4 degs. of unsaturation.

Regards,

JMB