Tips for organic deductive questions

Organic deductive questions

If the organic deductive questions gives the molecular formula, see if the number of C and H is comparable. In addition, if the molecule contains more than 6 carbon atoms, the compound is likely to contain a benzene ring.

Even if C and H is not comparable, the degree of unsaturation can tell us a lot. (Every two H lesser than the alkane general formula is one degree of unsaturation)

For example, one degree of unsaturation means that the compound either has one C=C or is cyclic. Two degree of unsaturation means
the compound could have one C=C and is cyclic, has two C=C bonds or one triple bond. Degree of unsaturation is also known as index of hydrogen deficiency.

Another vital piece of information is how many products a strong oxidative cleavage produces. If only one single product is formed with no loss in C, it means the the original compound is likely to be cyclic. If there is effervescence, the gas is likely to be carbon dioxide and the original compound contains terminal alkene. Be careful though, ethanedioic acid can also oxidize to 2 moles of carbon dioxide under strong oxidation conditions e.g. hot acidic potassium manganate (VII)

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