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I find it hard to remember which is "vinylic" and "allylic" carbon, so I feel it would be easier to remember if I know the reason why they are named so, like their word root origin or something like that. What is the historic origin of the term "vinylic" and "allylic"?

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Actually, word roots in organic chemistry aren't of much help because the origins have little connection with the actual molecular structure. There are entire books dedicated to these topics of you like chemical word origins.

Since allyl and vinyl are very common words, one cannot say that it was impossible to find the origins on the web. Search vinyl and etymology and you will get the desired results.

Allyl- implies coming from garlic. Still you will need to memorize the structure because those allylic compounds must have been found in garlic.

Vinyl- has the same fate. The name comes from German, derived from Vine, Vinegas (obsolete and uncharacteristic German: ethene) and -yl.

In short one has to memorize certain structures with common names.

Another puzzle in organic chemistry history is barbituric acid. It is allegedly stated that Barbara was the name of the German chemist's friend. Now how can one connect a lady's name with the structure of barbituric acid, if this were true?

Reference: Dictionary of Chemoetymology by A. Senning (Elsevier). The book is not online.

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Knowing the origin of the terms won't help you to identify what carbon is "allyic" or "vinylic". A vinyl group is a functional group with the formula $\ce{−CH=CH2}$ and allyl group is vinyl group but an extra methylene bridge ($\ce{-CH2}$), so it is $\ce{−CH2−HC=CH2}$. So, the carbons in vinyl group is "vinylic" carbon and the carbon in the extra methylene bridge is the "allylic" carbon.

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Regarding the origin of the word, the respective Wikipedia page has a good information. In short:

  • allyl comes from the scientific name for garlic, Allium sativum. In 1844, Theodor Wertheim isolated an allyl derivative from garlic oil and named it "Schwefelallyl".
  • vinyl comes from Latin vinum = "wine", and the Greek word "hylos" 'υλος (matter or material), because of its relationship with ethyl alcohol.
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