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naming of carbonyl compound

the book give me the compound name as phenylethanal , but i feel that the name should be 2-phenylethanal.... which is correct??
You leave off numbers if there's only one structural isomer possible.

1-phenylethanal would have a carbon with 5 bonds, so the only possible structure is with the phenyl on carbon 2.
Reply 2
Avatar for wilson dang
wilson dang
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Original post by KombatWombat
You leave off numbers if there's only one structural isomer possible.

1-phenylethanal would have a carbon with 5 bonds, so the only possible structure is with the phenyl on carbon 2.


so do you mean the ans should be phenylethanal??
Reply 3
Avatar for Pigster
Pigster
20
You won't be penalised for including the 2, but since it is unnecessary. we tend to leave it out.

Try drawing the displayed formula for 1-phenylethanal... you should realise KombatWombat's point.

Another example is ethanol, which you don't call ethan-1-ol, even though you perhaps should.
(edited 9 years ago)
Reply 4
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wilson dang
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Whete got 1-phenylethanal???? Do u mean the 2 is unnecessary because of phenylethanal has no isomer??
Reply 5
Avatar for Pigster
Pigster
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Whete? (www.urbandictionary.com/define.php?term=whete didn't help!?!)

The various methyl benzaldehydes (and many others) are isomers of phenylethanal.

One doesn't have to state which carbon the phenyl group is attached to on the ethanal carbon chain, since it cannot attach to carbon 1, therefore it must attach to carbon 2.

Another example is methypropanal. Which perhaps should be called 2-methylpropanal, but can you have 1-methyl or 3-methyl? No, so the numbering is usually dropped.

We're a lazy bunch us chemists, sometimes.

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