IUPAC nomenclature Dr Margaret A.L. Blackie

Naming of the Alkanes

Naming of the alkanes 2. Identify the longest unbroken carbon chain 8 – carbon chain7 – carbon chain octane base 1. Identify the main functional group This step is not necessary for the alkanes – there is no functional group.

First substituent at carbon no Number the chain so that the first substituent has the lowest possible number First substituent at position no. 3 Correct numbering: Substituents at 2, 5 and 6 NB: If the first substituent (side chain) has the same number, use the second substituent to separate the two etc …

Identify the substituents (side chains and the position on the main chain or ring) 2-methyl 5-ethyl 6-methyl

5. Use the prefixes (di-, tri-, tetra-) depending on the number of identical substituents bonded to the main chain methyl 5-ethyl 6-methyl 2,6-dimethyl 5-ethyl

Write down the side chains in alphabetical order, preceded by the number: (don’t write down di-, tri-, tetra-etc. in alphabetical order) 5-ethyl-2,6-dimethyloctane Dimethyl comes after ethyl, because e is before m – the d of di is not considered.

5-ethyl-2,6-dimethyloctane The name should not be separated (there are some exceptions which will be addressed later.) Dimethyloctane is written as one word Numbers separated from words by a hyphen (N shows a position and is considered as a number when naming the amines and amides) Numbers separated by a comma Note: The name is WRONG if any one of these three rules are disobeyed!

5-ethyl-2-6-dimethyloctane 5,ethyl,2,6,dimethyloctane 5-ethyl-2,6-dimethyl octane Important: The name is WRONG if any one of these rules are disobeyed! 5-ethyl-2,6-dimethyloctane Name is wrong – the hyphen between the numbers are incorrect The name is wrong – the comma between a number and a word is incorrect Name is wrong – There should be no space between dimethyl and octane What is wrong with the names below?

Important points for purposes of explanation

The longest unbroken carbon chain is not necessarily straight Longest straight chain contains only 5 carbons Longest unbroken chain contains 8 carbons Therefore the name is octane and not pentane

If there are two options for an unbroken carbon chain: Choose the chain with the most side chains as the base Three substituentsTwo substituents Correct name: 2,6-dimethyl-4-propyloctane Incorrect: 3-methyl-5-isobutyloctane

If there is no difference in the number of the position of the first side chain, look at the following side chain, if there is no difference at the second, look at the third, etc First substituent is at position 2 in both numberings Second substituent at positions 3 and 4 respectively. Correct numbering Correct name : 2,3,5-trimethylhexane

When there is no difference in the numbers of the positions of the substituents : choose the numbers according to alphabetical order of the substituents, that is the first substituent alphabetically gets the lowest number methyl-4-ethylhexane 3-ethyl-4-methylhexane Correct name

When a functional group occurs

Identifying the main functional group is the first step in naming the compound. At grade 12 level the following step is unnecessary, but is included for educators. Functional groups are prioritised according a list (see next slide) The main functional group is the functional group with the highest priority. The base is the longest unbroken carbon chain containing the main functional group.

FUNCTIONAL GROUPS Highest to lowest priority General nameGeneral structure Name as suffix Carboxylic acid-oic acid Ester-oate Aldehyde -al Ketone-one Alcohol-ol Alkene-ene Alkyne-yne

The highest priority group must get the lowest possible number Number from left to right Main functional group – ketone – suffix ‘one’ Longest unbroken carbon chain containing the main functional group – 5 carbons - ‘pentane’ Base – pentan-2-one Subsituents: 3-bromo 4-methyl Correct name: 3-bromo-4-methylpentan-2-one

correct name: 3-bromo-4-methylpentan-2-one bromo-4-methyl-2-pentanone is also acceptable It is better to write the number directly in front of the main functional group

Correct name: 3-bromo-4-methylpentan-2-one Consider: Main functional group – ketone – prefix ‘one’ Longest unbroken carbon chain containing the main functional group – 5 carbons – unsaturated chain - ‘pentene’- Base – pent-4-ene-2-one correct name: 3-bromo-4-methylpent-4-ene-2-one

Number or no number? Main functional group : aldehyde – prefix ‘al’ correct name: Pentanal Main functional group: ketone – prefix ‘one’ correct name: Pentan-2-one No number on the aldehyde because the carbonyl group must be on the first carbon Number necessary because the carbonyl group can be at position 2 or 3 Revise: the main functional group always gets the lowest possible number. The carbonyl group is always at the end or beginning of the chain, therefore it must be in position number 1. Pentan-1-al is NOT acceptable

Number or no number? correct name: But-2-ene correct name: Propene But-1-ene is a possibility, so the number is important.‘ There is no alternative, propene is prop-1-ene The locant is redundant in this particular case and should be dropped. The redundancy is associated with this particular molecule not the nature of the functional group so inclusion of the locant is acceptable

Questions 1.On the previous slide But-2-ene and But-1-ene are called… ? 2.Give a brief explanation for the names given in question 1. 3.Write down the molecular formula for the above compounds. 4.Write down the structural formulae for 2 more possible structures. 5.Name the structures completed in question 4. Answers 1. ISOMERS 2.Isomers are compounds with the same molecular formula but different structural formulas. 4. Write down the structural formulae for 2 more possible structures. 2-MethylPropene C CC H H HH HH H H CH 2 CH 3 C C HC Cyclobutane

Carboxylic acids and derivatives Carboxylic acids Propanoic acid Propanoate ion Propanoyl chloride (not for exam)

Esters Methylpropanoate Identify carboxylic acid that produces the ester This part is named as with the corresponding ion - propanoate Identify the substituent on the carboxylate oxygen This part is named as the alkyl group – methyl