Before IUPAC nomenclature, in the old system of alkane and alcohol nomenclature, the straight chain alkane was called the n-alkane, or normal alkane. For example, n-butyl alcohol would now be called 1-butanol, and n-butane would simply be called butane. sec meant secondary, which for an alcohol meant the OH was a secondary alcohol, and for an alkane meant that one methyl group had been moved to a secondary position - so sec-butyl alcohol would now be called 2-butanol and sec-butane would be called 2-methylpropane. tert meant tertiary, so the alcohol was on a tertiary carbon - tert-butyl alcohol or t-butyl alcohol l would now be called 2-methyl-2-propanol.
Iso was sort of a catch-all - it was the "other isomer". It came to mean an isomer that add a dimethyl methine at one end, like an isopropyl group. So 2-propanol was more commonly called isopropyl alcohol than sec-propyl alcohol. Isobutyl alcohol was the alcohol that wasn't n-, sec-, or tert-butyl alcohol, which would now be called 2-methyl-1-propanol. Isoamyl alcohol was the five carbon analog, 3-methyl-1-butanol.
Neo was also used, being the isomer with a t-butyl group at one end. Neopentyl alcohol was the smallest of these, 2,2-dimethyl-1-propanol. The system of common names quickly got clunky and required a lot of memory work as more carbons were added, which is one reason we have an IUPAC system of systematic nomenclature now.
You can see the common names for the 5-carbon alcohols here, which will give you some idea of the problems involved:
http://en.wikipedia.org/wiki/Amyl_alcohol
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Topic: O-Chem help: what is iso (Read 3028 times)