Shouldn't this compound be called 2-methyl-5-(1,2-dimethylpropyl)nonane? The book says that the name should have dimethylpropyl methyl nonane in that order. Shouldn't the methyl group come first since methyl comes before methylpropyl (in the alphabetic order)? Our prof told us to ignore prefixes such as mono, di, tri when putting groups in alphabetic order.
‘5-(1,2-Dimethylpropyl)-2-methylnonane’ is not the preferred IUPAC name. The preferred name according to current IUPAC recommendations is 2-methyl-5-(3-methylbutan-2-yl)nonane.
If this is a homework exercise, however, it might be based on obsolete IUPAC recommendations from 1979 or 1993.
You are partly correct; simple prefixes are arranged alphabetically disregarding any multiplicative prefixes. The multiplicative prefixes are inserted later and do not alter the alphabetical order. For example, ‘1,2-dibromo-’ is considered to begin with ‘b’.
However, the name of a compound substituent is considered to begin with the first letter of its complete name. For example, ‘1,2-dibromobutyl-’ is considered to begin with ‘d’.
Likewise, ‘1,2-dimethylpropyl-’ is considered to begin with ‘d’. Therefore, it is arranged before ‘methyl’.