Ochem - Please confirm IUPAC understanding

[RCT PC CRN]

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C-C-C-C ---- 4 c chain

From left to right, if I have -Cl on second C and -I on third then I would number C1-C2-C3-C4 (Left to Right) - cause it will be 2,3 either way but alphabetically Left to Right make sense. IUPAC name: 2-chloro-3-iodobutane

If I change -I to -Br then I would number C4-C3-C2-C1 (Right to Left) cause now -Br is higher up in alphabets. IUPAC name: 2-bromo-3-chlorobutane.

Above is true for any substituents of same group (i.e. when numbering is same either way you number the chain according to alphabets not to MW)

One more example, If I change -I to -CH3 (methyl) then numbering stay same C1-C2-C3-C4 (Left to Right). IUPAC name: 2-chloro-3-methylbutane.

Above rule doesn't hold when there is 2 different group of substituents. In that case priority of group kicks in. e.g. If I change -I to -OH (hydroxy). IUPAC name: 3-chloro-2-butanol (3-chloro-2-hydroxybutane). If I number the chain thinking -chloro is higher up in alphabets then -hydroxy then incorrect name would be 2-chloro-3-butanol (2-chloro-3-hydroxybutane). Since -Cl and -OH is two different group, -OH group takes priority over halide group.

Please confirm my understanding. Thanks.

 

[casper22]

U have nailed it right.

 

[skylark]

is naming IUPAC common for the ochem section? How much time should we spend on studying the rules?

Should we also know common names of structures (as outlined in the Kaplan book) such as Aniline, Anisole, sec-butyl, etc?

 

[trevnichols22]

I would know both, however I would concentrate on the IUPAC system as that is it can be used for all structures. The rules are quite simple really.