I was solving questions on the MSU website on organic nomenclature. Out of the following questions, I got only the first and last one right.enter image description here Where am I going wrong with the others?Hints would suffice.

EDIT:I got the second one correct as well.



Indeed, most of the names proposed by you correspond to the preferred IUPAC names in accordance with the current version of Nomenclature of Organic Chemistry – IUPAC Recommendations and Preferred Names 2013 (Blue Book):

(1) 3-bromo-2,5-dimethylhexane

(2) 7,7-dichloro-4-ethyl-3,3,8-trimethyl-4-propyldecane (your edit is correct)

(3) see below

(4) 2-chloropent-1-en-4-yne

(5) 1-bromo-3-ethyl-5-methylbenzene

For compound (3), you have to consider the relevant rules for the numbering of locants for substituent prefixes:


When several structural features appear in cyclic and acyclic compounds, low locants are assigned to them in the following decreasing order of seniority:


(f) detachable alphabetized prefixes, all considered together in a series of increasing numerical order;

(g) lowest locants for the substituent cited first as a prefix in the name;


Note that Rule (f) takes precedence over Rule (g).

In accordance with Rule (f), compound (3) could be named as 5-bromo-1-methylcyclohexa-1,4-diene (which was your proposal) as well as 1-bromo-5-methylcyclohexa-1,4-diene since both names correspond to the locant set ‘1,5’. However, according to Rule (g), this example is named as 1-bromo-5-methylcyclohexa-1,4-diene rather than 5-bromo-1-methylcyclohexa-1,4-diene since bromo is cited first as a prefix in the name.



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