Let's consider the following compound:

  1. $\ce{CH3-CH2-CH(CH3)-CH2-CH2-CH(CH(CH3)-CH(CH3)-CH2-CH(CH3)3)}$

Its IUPAC name is 2,2,7-trimethyl-4-(1-methyl-propyl)-nonane

  1. $\ce{CH3-CH2-CH(C2H5)-C(CH3)(C(CH3)3)-CH2-CH2-CH(CH3)-CH2-CH2-CH3}$

Its IUPAC name is 3-ethyl-4,7-dimethyl-4-(1,1-dimethyl-ethyl)-decane

I wish to ask if the following names are acceptable (respectively):

  1. 4-(1-methyl-propyl)-2,2,7-trimethyl-nonane
  2. 4,7-dimethyl-4-(1,1-dimethyl-ethyl)-3-ethyl-decane

Do complex substances follow a rule regarding where they should be placed in the IUPAC name or can they be placed anywhere?
Do prefixes like bis, tris, tetrakis, etc. need to be considered while naming?

  • 1
    $\begingroup$ The suggested names “2,2,7-trimethyl-4-(1-methyl-propyl)-nonane” and “3-ethyl-4,7-dimethyl-4-(1,1-dimethyl-ethyl)-decane” seem to be based on obsolete IUPAC recommendations from 1979. The preferred names according to current (2013) IUPAC nomenclature are 4-(butan-2-yl)-2,2,7-trimethylnonane and 4-tert-butyl-3-ethyl-4,7-dimethyldecane, respectively. $\endgroup$ – Faded Giant Mar 30 '18 at 11:41

Okay so here is the situation: You have two subsitutions, methyl and 1-methylpropyl as the two substituents here. You wish to know in which order the substituents must be written in the name. You knew that substituents are arranged alphabetically, and both methyl and 1-methylpropyl start with the same letter m.

Consider a dictionary. It has over thousands of words that start with the letter C. But we can still arrange the words in order by looking at the second, third, fourth, fifth, etc. letters of the names. Similarly, if the first letters are the same, look at the second, third and fourth letters.

Here's where we arrive at the conclusion. methylpropyl will be ranked below methyl as per dictionary order. Thus the name of the compound would, in fact, be 2,2,7-trimethyl-4-(1-methyl-propyl)-nonane and the other name is not accepted.

I believe you can continue from here to name the second compound.

Important notes:

  1. The inclusion of di, tri in the name must only be applied for complex subsituents such as in the case of 5-(dimethylethyl)decane. In cases such as 4-ethyl-5,5-dimethyldecane, do not use d as the starting letter. This is becase d is not the part of the name of the subsitituent (methyl) and only indicates how many times this subsitituent occurs in the compound.

  2. Do not add hyphens between methyl and decane such as "methyl-decane". Use "methyldecane" Hyphens must only be used between numbers and subsituents for which the number represents its position in the name.

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  • $\begingroup$ So prefixes like di, tri, tetra, etc need to be considered in complex substituents? $\endgroup$ – J_B892 Mar 29 '18 at 3:43
  • $\begingroup$ Exactly. It must be considered where it is a part of the name. (dimethylethyl) is the complete name of the substituent and hence d is considered as the starting letter. $\endgroup$ – Pritt says Reinstate Monica Mar 29 '18 at 4:01
  • $\begingroup$ This is strictly for complex substituents right?(Just clarifying) $\endgroup$ – J_B892 Mar 29 '18 at 7:18

Substituents are always written in alphabetical order (without considering the numerical prefixes such as di, tri, etc). Also, in case of trimethyl and methyl propyl, having same first alphabet (i.e. m), generally the substituent with shotter name is written first. But as per my knowledge, there is no such official rule. So the name that you have suggested for the first case is acceptable. But your second name is incorrect as alphabetical order is not considered.

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  • $\begingroup$ 1. 2,2,7-trimethyl-4-(1-methyl-propyl)-nonane 2. 3-ethyl-4,7-dimethyl-4-(1,1-dimethyl-ethyl)-decane Is this right? $\endgroup$ – J_B892 Mar 28 '18 at 12:05
  • $\begingroup$ Yes. That's correct. $\endgroup$ – Jasgeet Singh Mar 28 '18 at 12:06

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