C C-C4-k-R.
Both features can be included in the mole-
I
C C I cule, c-C-C-C-C-C;
y-cleavage will explain the presI C ence of 3,3-dimethyl-l-pentene,
C
C
I I
c--c--c-c-c
f
I I
C
The alkane is 3,3-dimethylhexane. Monosubstituted alkanes and gem structures can be rather easily identified. Other polysubstituted compounds are more challenging but usually these can be handled also. Example 3 is illustrative of this situation. Example 3. Olefin composition is: propene, 7.1 %; isobutene/l-butene, 66.0%; 3-methyl-2-pentene, 0.5 %; 4,4-dimethyl-2-pentene, 3.3 %; 3-methyl-l-butene, 0.1 %; 3,4-dimethyl-1-pentene, 0.3 %. The dominant olefin is the isobutene/l-butene group but it can be assumed that the olefin is isobutene (1-butene is not found at a concentration >22 % based on an assumption exC plained earlier). This indicates a C-C-
I
structure. For a
c C
I I
structure like, C-C-C-C-C-,
y-cleavage would give the
C C
I I
This olefin is absent; therefore, it can
C be presumed that a different gem olefin is formed by y-cleavage. Fragmentation of the compound, C
C
I I c-c-c-c f c c-c-c=c-c I I I C
RECEIVED for review December 28, 1970. Accepted March 30, 1971.
c + c-c-c-c=c
C
olefin, C-C-C=C.
The large concentration of 2-methyl-2-butene suggested 2,3or 2,3,4- structures. No 2,3-dimethyl-l-butene is reported, which would seem to rule out a 2,3-dimethyl configuration. The presence of 2-butene at 5.8 indicated that the molecular formula would have to explain this olefin. There were two constraints: neither a pendant ethyl nor butyl group was present. These overall requirements could not be met. A subsequent check showed the compound to be 2,3,4-trimethylpentane. Presence of the relatively large amount of 2-butene negated a correct identification.
C
C
(4,4-dimethyl-2-pentene) explains the only observed gem olefin. This structure meets the constraint that no pendant ethyl group exists (ethene is absent). Small concentrations of other, even unpredicted, olefins can be ignored, as this is a common occurrence. Example 4. Olefin composition is: ethene, 0.6%; propene, 26.1 %; isobutene/l-butene, 0.6%; 2-butene, 5.8%; 3-methyl-l-butene, 3.4%; 2-methyl-2-butene, 28.8 %; plus miscellaneous others of
