Ring Strain
Mixing solid iodine and cyclohexene shows little reaction but
mixing iodine and 
-pinene
produces a very vigorous exothermic reaction and sublimation of
solid iodine to dense iodine vapor.
Keywords
descriptive chemistry, alkenes, iodine, alpha-pinene
(-pinene),
thermodynamics, organic, bonding, real life/environment
Multimedia
Demonstration
_Play
movie (25 seconds, 1.5 MB)
Iodine crystals are poured into a large cylinder. Like most
alkenes, cyclohexene reacts only sluggishly with iodine. But when
-pinene
is poured into iodine, the exothermic reaction vaporizes iodine.
The extra energy comes from relief of ring strain in the
-pinene
molecules.
Historical Note
_Play
movie (15 seconds, 0.9 MB)
In the past, as a form of antisepsis, veterinarians used the
reaction of iodine with turpentine (which is 60% -pinene)
to force iodine into the deep wounds of large animals.
Discussion
There are several common pronounciations of the word 'iodine'. Variations of the movies are provided with the following:
Demonstration
Version where
'Iodine' rhymes with 'chlorine'
Version where 'Iodine'
rhymes with 'mine'
Historical Note
Version where
'Iodine' rhymes with 'chlorine'
Version where 'Iodine'
rhymes with 'mine'