The electron impact mass spectra of several new cycloalkane-substituted pyr
imidines are reported. The cleavage of the cycloalkanepyrimidines depends s
trongly on the alkyl ring size and on the substituents attached to this rin
g. The pyrimidines with fused small rings (cyclobutapyrimidines) undergo co
nsecutive elimination of two nitrile molecules affording cyclobutadiene. Ho
wever, for the pyrimidines with rings larger than cyclobutane, the main fra
gmentation observed involves ring opening with loss of alkyl radicals, The
substituents with strong electronic effects attached to the alkyl ring prom
ote a different cleavage mechanism with elimination of these groups. Copyri
ght (C) 1999 John Wiley & Sons, Ltd.