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I'm only familiar with Alkanes at a basic level currently. What seems logical to me is that an Alkyl molecule with the:

"iso" prefix means its an isomer of that alkyl, the usual way i'd see it would be the alkyl group with a substituent (the way an hexane could be isopentane if I got it right)

as for the "sec" prefix, the alkyl group is connected to the main molecule through a secondary carbon (meaning the carbon on the alkyl is bonded with two other carbons in the alkyl, no consideration given to the main chain here)

I find the "tert" prefix similar to the latter, it is connected to the maine chain through a tertiary carbon (bonded with three carbons on the alkyl)

I couldn't find a basic logical way to address the definition of the "neo" prefix.

Are the ways I described the rest of the prefixes correct?

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    $\begingroup$ Sec- and tert- are exactly what you say they are. There's no good way to understand the others. Consider that leucine has a isobutyl group, but isoleucine has a sec-butyl group. $\endgroup$
    – Zhe
    Mar 16, 2019 at 17:34
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    $\begingroup$ chemistry.stackexchange.com/questions/98362/… $\endgroup$
    – Mithoron
    Mar 16, 2019 at 20:04

1 Answer 1

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The prefixes, iso-, sec-, tert-, neo- are all traditional names when structural organic chemistry was still developing. You have already rationalized all except neo-. Neo- is Greek term for new. I looked up the OED etymological dictionary for older meanings, and the earliest use is traced to 1876. Now you can see in no 2, that neo- was a good option.

  1. Used in the names of chemical compounds, minerals, etc., which are closely related to, or new forms of, known substances. neocatechu n. (Obsolete) a kind of catechu.

  2. Used in the names of compounds and radicals in which one carbon atom is linked to four others. Not part of standard chemical nomenclature although well established in neohexane and neopentane (and related terms). (a) Categories »

† neo-acid n. Obsolete 1876 W. Odling in London, Edinb., & Dublin Philos. Mag. 5th Ser. 1 216 The names which call to mind that the normal, iso-, and neo-acids are mono-, di-, and trimethyl & etc. derivatives would seem to be most advantageous.

Neo- even it is used today represents a terminal tert-butyl group, just like the prefix iso- represents a iso-propyl group at the end.

IUPAC names have superseded all.

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    $\begingroup$ I only regularly see "neo" as a prefix to indicate neopentane derivatives such as neopentylamine $\endgroup$
    – AlmostCatlike
    Mar 17, 2019 at 13:03

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