IUPAC names of branched saturated hydrocarbons

Any branch or side chain hanging off a saturated parent hydrocarbon is itself an ALKYL group (an alkyl substituent). Before the rules for naming a whole branched alkane can be given, the alkyl groups themselves need names. A STRAIGHT-CHAIN alkyl group is generated, conceptually, by removing exactly one hydrogen atom from the terminal carbon of a straight-chain alkane, and is named simply by swapping that alkane's '-ane' ending for '-yl' -- so methane (CH4) gives methyl (-CH3, abbreviated Me), ethane gives ethyl (-CH2CH3, Et), propane gives propyl (-(CH2)2CH3, Pr), butane gives butyl (-(CH2)3CH3, Bu), and so on up the series (decane gives decyl, -(CH2)9CH3); the aromatic analogue, the phenyl group (C6H5-), is likewise commonly abbreviated Ph. A BRANCHED alkyl group instead comes from removing a hydrogen from some NON-terminal carbon of an alkane, or from any carbon of an already-branched alkane; the four smallest and most commonly encountered branched alkyl groups keep their own accepted trivial names, which are simply used directly inside full IUPAC names rather than being derived systematically each time: isopropyl (CH3-CH(-)-CH3, the point of attachment on the middle carbon), isobutyl (CH3-CH(CH3)-CH2-), sec-butyl (CH3-CH(-)-CH2-CH3, attachment on the second carbon), and tert-butyl (CH3-C(CH3)2-, a fully branched central carbon carrying three methyls plus the attachment point). With the alkyl groups themselves named, a full branched-chain alkane is named by six rules working together. RULE 1: identify the longest continuous carbon chain in the molecule -- this becomes the PARENT chain, and every carbon not part of it is a substituent; if two candidate chains tie for the same (longest) length, the one carrying the GREATER number of substituents is chosen as the true parent chain. RULE 2: number that parent chain from whichever end gives the LOWEST possible locant number(s) to the substituent position(s). RULE 3: list every substituent's name, in alphabetical order, as a prefix to the parent alkane's name, each one preceded by its own locant number and a hyphen -- so a chain bearing an ethyl group at position 4 and a methyl group at position 3 is named 4-ethyl-3-methylheptane (ethyl cited first, alphabetically, even though its locant number is larger), never '3-methyl-4-ethylheptane'. RULE 4: if numbering from either end of the parent chain happens to give the exact SAME overall set of locant numbers, choose whichever direction gives the LOWER locant specifically to the substituent that comes first alphabetically -- so a chain with tied locant sets for an ethyl and a methyl substituent is named 3-ethyl-4-methylhexane (giving ethyl, which is alphabetically first, the lower number 3), not '3-methyl-4-ethylhexane'. RULE 5: where two or more IDENTICAL substituents are present, a multiplying prefix -- di- (2), tri- (3), tetra- (4), and so on -- is placed immediately before that substituent's name, and the individual locant numbers of every one of those identical substituents are listed together, separated by commas, with exactly as many numbers given as there are substituents of that kind; when alphabetising substituent names for citation order, the multiplying prefixes di-, tri-, tetra- themselves are IGNORED (so, for instance, 'isopropyl' is alphabetised ahead of 'methyl', since 'i' precedes 'm', while 'sec-' and 'tert-' are likewise ignored for alphabetising purposes); the finished substituent-plus-parent name is wr …