C n H 2n+2 Alkanes: Methane, Ethane, and Propane

Methane (CH 4 ) CH 4 Ethane (C 2 H 6 )CH 3 CH 3 Propane (C 3 H 8 )CH 3 CH 2 CH 3 bp -160°C bp -89°C bp -42°C The Simplest Alkanes

C 4 H 10 Isomeric Alkanes: The Butanes

ButaneCH 3 CH 2 CH 2 CH 3 Isomer of butane(CH 3 ) 3 CH bp -0.4°C bp -10.2°C

Higher Alkanes

CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 Pentane Hexane CH 3 CH 2 CH 2 CH 2 CH 3 CH 3 CH 2 CH 2 CH 2 CH 2 CH 2 CH 3 Heptane

The C 5 H 12 Isomers

Pentane CH 3 CH 2 CH 2 CH 2 CH 3 Isomer of pentane (CH 3 ) 2 CHCH 2 CH 3 Neopentane (CH 3 ) 4 C C 5 H 12

How many isomers? The number of isomeric alkanes increases as the number of carbons increase. There is no simple way to predict how many isomers there are for a particular molecular formula.

Number of Constitutionally Isomeric Alkanes CH 4 1 C 2 H 6 1 C 3 H 8 1 C 4 H 10 2 C 5 H 12 3 C 6 H 14 5 C 7 H 16 9 C 8 H C 9 H C 10 H C 15 H 32 4,347 C 20 H ,319 C 40 H 82 62,491,178,805,831

Systematic Nomenclature International Union of Pure and Applied Chemistry IUPAC Committee on Organic Nomenclature

The alkanes

Nomenclature of the Alkanes Alkanes always have the ending -ane. Side chains (substituents) are named as alkyl groups.

Common alkyl groups (C 1 through C 4 )

IUPAC nomenclature of alkanes identify the longest chain -- parent number from the end closest to first branch Name the groups attached to the chain, using the carbon number as the locator. Alphabetize substituents. Use di-, tri-, etc., for multiples of same substituent combine number and name of substituent with parent name, separating with hyphen

Longest Chain The number of carbons in the longest chain determines the base name: ethane, hexane. If there are two possible chains with the same number of carbons, use the chain with the most substituents. =>

Number the Carbons Start at the end closest to the first attached group. If two substituents are equidistant, look for the next closest group

Organic nomenclature methylbutane

Find the longest continuous carbon chain methylpentane

You must choose the longest continuous carbon chain ethylheptane

IUPAC rules 1. Find the longest straight chain = parent chain 2. Number the parent chain in the direction that gives the lowest number to the substituents at the first point of difference. 3. Two or more identical groups are indicated by di, tri, tetra, etc. Longest chain is 7 (not 6). This is 3-methylheptane.. 2,3,6-trimethylheptane (not 2,5,6-trimethyl heptane) 2,2,6,6,7-pentamethyloctane (not 2,3,3,7,7-pentamethyloctane)

4. Different groups are listed in alphabetical order (di, tri, tetra, etc. don’t count; n, sec, tert don’t count; iso does). 5. If the numbering is the same in both directions, choose the numbering to follow the alphabetical order. IUPAC rules 6-ethyl-5-isopropyl-2,2-dimethyloctane 5-ethyl-6-methyldecane

6. When two or more chains compete for the longest, the choice goes to the one with the greater number of side groups. IUPAC rules 2,4,6-trimethyl-5-propyloctane

Number from the end nearest the first substituent ethyl-3-methylheptane

Number from the end nearest the first substituent ethyl-5-methyloctane

Use “di-” with two substituents ,3-dimethylbutane

Every substituent must get a number ,3-dimethylhexane

Number from the end nearest first substituent ,7,8-trimethyldecane

Number from the end which has the “first difference” ,4,8-trimethyldecane

A More-Highly-Substituted Carbon Takes Precedence ,2,4-Trimethylpentane

Which end do we number from? ethyl-6-methyloctane

IUPAC rules 6-ethyl-2,2,5,7-tetramethylnonane (not 6,7-diethyl-2,2,5-trimethyloctane. 7-tert-butyl-8-isobutyl-4-isopropyldodecane (hyphenated words aren’t alphabetized). OR 7-(1,1-dimethylethyl)-4-(1-methylethyl)- 8-(2-methylpropyl)dodecane Name the following compounds.

Good Luck! 7-(1,1-Dimethylbutyl)-3-ethyl-7-methyldodecane

Branched Substituents isopropyl sec -butylisobutyl tert -butyl ( t -butyl) neo -pentyl

Halogens and other side groups Flouro –F Chloro –Cl Bromo –Br Iodo –I Nitro –NO 2

Bromoethane “Ethyl bromide”

2-Chloro-2-methylpropane “tert-Butyl chloride”

2-Bromo-3-methylpentane

Complex Substituents If the branch has a branch, number the carbons from the point of attachment. Name the branch off the branch using a locator number. Parentheses are used around the complex branch name methyl-3-(1,2-dimethylpropyl)cyclohexane =>

The isopropyl group can be named as a “complex” substituent 1-methylethyl

If you can name this, you can name almost anything! isopropyl-2,6,6-trimethylnonane

Now, rename the isopropyl group. Notice the alphabetical order! ,6,6-trimethyl-4-(1-methylethyl)nonane

Naming complex substituents -- this one is alphabetized under d 1,3-dimethylbutyl

deciding on alphabetical order for complex groups Complex groups are alphabetized under the first letter of the name (1,3-dimethylbutyl) = d (1,1,2-trimethylpropyl) = t (1-ethyl-1,2-dimethylbutyl) = e

Naming complex substituents 2-ethyl-1,1-dimethylbutyl

This Should Be Fun (1-Ethyl-1-methylpropyl)-5-propylnonane

name this two ways -- (the complex group) 7-(1,1-dimethylethyl)-3-ethyl-7-methyldecane 7-tert-butyl-3-ethyl-7-methyldecane

Common Nomenclature Pitfalls Did not find the longest carbon chain Numbered chain from the wrong end Forgot to repeat number for each identical substituent; forgot to use di- tri- tetra-, etc. Used “iso”, “sec”, or “tert” as part of a parent name Confusing propyl / isopropyl, etc. Writing the name as more than one word Incorrect punctuation

degree of substitution

Degree of Substitution 1° 1° 1° 3° 2° 3° 2° 4° 1° 1° 3° 2° 1° 2° 1°

Block diagram for nomenclature

cyclic molecules

Nomenclature for Cyclic Alkanes For compounds with a single ring, add the prefix “cyclo-” to the root name for the alkane comprising the ring.

Nomenclature of the Substituted Cycloalkanes If there is only one substituent, do not use the “1”. If there is more than one substituent, you must use all numbers, including “1”! Number around the ring in a direction to get from the first substituent to the second substituent by the shorter path. For equivalent degrees of substitution, number in a direction that follows the alphabetical sequence. A carbon with greater substitution has precedence in numbering.

Bromocyclopropane

1,1-Dimethylcyclohexane

4-Ethyl-1,1-dimethylcyclohexane

Two ways of naming this 1-isopropyl-2-methylcyclohexane 1-methyl-2-(1-methylethyl)cyclohexane

Numbering Starts at the Most Highly-Substituted Carbon Chloro-1,1,6-trimethylcycloheptane

cycloalkyl groups

3-Cyclobutyl-3-methylpentane

2-Cyclobutylbutane sec-Butylcyclobutane

Name the following cycloalkanes. Check your answers by clicking on the arrow. IUPAC rules 1,1,2-trimethycyclohexane 4-cyclopentyl-2,3-dimethylhexane 1,2-dicyclopropylethane