CCnnHH22nn+2+2

Introduction to Alkanes:Methane, Ethane, and Propane

Methane (CH4) CH4 Ethane (C2H6) CH3CH3

Propane (C3H8) CH3CH2CH3

bp -160°Cbp -160°C bp -89°Cbp -89°C bp -42°Cbp -42°C

The Simplest Alkanes

CC44HH1010

Isomeric Alkanes: The Butanes

n-Butane CH3CH2CH2CH3

Isobutane (CH3)3CH

bp -0.4°Cbp -0.4°C bp -10.2°Cbp -10.2°C

Higher n-Alkanes

CHCH33CHCH22CHCH22CHCH22CHCH22CHCH33

nn-Pentane-Pentane

nn-Hexane-Hexane

CHCH33CHCH22CHCH22CHCH22CHCH33

CHCH33CHCH22CHCH22CHCH22CHCH22CHCH22CHCH33

nn-Heptane-Heptane

The C5H12 Isomers

nn-Pentane-Pentane

CHCH33CHCH22CHCH22CHCH22CHCH33

IsopentaneIsopentane

(CH(CH33))22CHCHCHCH22CHCH33

NeopentaneNeopentane

(CH(CH33))44CC

CC55HH1212

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

CH4 1 C2H6 1 C3H8 1 C4H10 2 C5H12 3 C6H14 5 C7H16 9

C8H18 18 C9H20 35 C10H22 75 C15H32 4,347 C20H42 366,319 C40H82 62,491,178,805,831

Systematic NomenclatureSystematic Nomenclature

International Union of Pure and Applied Chemistry

IUPACCommittee on Organic Nomenclature

The alkanes The alkanes Methane (CH4)

Ethane (C2H6)

Propane (C3H8)

Butane (C4H10)

Pentane (C5H12)

Hexane (C6H14)

Heptane (C7H16)

Octane (C8H18)

Nonane (C9H20)

Decane (C10H22)

CH4

CH3 CH3

CH3 CH2 CH3

CH3 CH2 CH2 CH3

CH3 CH2 CH2 CH2 CH3

CH3 CH2 CH2 CH2 CH2 CH3

CH3 CH2 CH2 CH2 CH2 CH2 CH3

CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH3

CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3

CH3 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH2 CH3

Nomenclature of the AlkanesNomenclature of the Alkanes

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

alkyl groups.

Common alkyl groupsCommon alkyl groups (C (C11 through C through C44))

CH3

CH3 CH2

CH3 CH2 CH2

CH3 CH2 CH2 CH2

Methyl

Ethyl

Propyl

Butyl

Isopropyl

Isobutyl

(1-Methylethyl)

(2-Methylpropyl)

sec-Butyl(1-Methylpropyl)

tert-Butyl(1,1-Dimethylethyl)

CH3 CH

CH3

CH3 CH CH2

CH3

CH3 CH2 CH

CH3

CH3 C

CH3

CH3

IUPAC nomenclature of alkanesIUPAC 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.

C

CH3

CH2

CH3

CH CH2 CH2 CH3

CH CH2 CH3H3C

H3C

=>

Number the Carbons Start at the end closest to the first attached

group. If two substituents are equidistant, look for

the next closest group.

1

2

3 4 5

6 7CHH3C

CH3

CH

CH2CH3

CH2 CH2 CH

CH3

CH3

CH3 CH2 CH CH3

CH3

Organic nomenclatureOrganic nomenclature

4 3 2 1

2-methylbutane

CH3 CH2 CH CH3

CH2 CH3

Find the longest continuousFind the longest continuouscarbon chaincarbon chain

1 2 3

4 5

3-methylpentane

CH3 CH2 CH CH2 CH2 CH3

CH2 CH2 CH3

You must choose the longestYou must choose the longestcontinuous carbon chaincontinuous carbon chain

4 3 2 1

5 6 7

4-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.

CH3 CH2 CH2 CH2 CH

CH2 CH3

CH3Longest 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

CH3 CH2 CH2 CH CH CH2 CH3

CH3

CH2 CH3

Number from the end nearestNumber from the end nearestthe first substituentthe first substituent

7 6 5 4 3 2 1

4-ethyl-3-methylheptane

CH3 CH2 CH2 CH CH2 CH CH2 CH3

CH2 CH3

CH3

Number from the end nearestNumber from the end nearestthe first substituentthe first substituent

8 7 6 5 4 3 2 1

3-ethyl-5-methyloctane

CH3 CH CH CH3

CH3

CH3

Use “di-” with two substituentsUse “di-” with two substituents

1 2 3 4

2,3-dimethylbutane

CH3 CH2 C CH2 CH2 CH3

CH3

CH3

Every substituent must get a numberEvery substituent must get a number

1 2 3 4 5 6

3,3-dimethylhexane

CH3 CH2 CH CH CH2 CH2 CH2 CH2 CH CH3

CH3CH3

CH3

Number from the end nearestNumber from the end nearestfirst substituentfirst substituent

10 9 8 7 6 5 4 3 2 1

2,7,8-trimethyldecane

CH3 CH2 CH CH CH2 CH2 CH2 CH CH2 CH3

CH3

CH3

CH3

Number from the end which hasNumber from the end which hasthe “first difference”the “first difference”

1 2 3 4 5 6 7 8 9 10

3,4,8-trimethyldecane

CH3 CH CH2 C CH3

CH3 CH3

CH3

A More-Highly-SubstitutedA More-Highly-SubstitutedCarbon Takes PrecedenceCarbon Takes Precedence

5 4 3 2 1

2,2,4-Trimethylpentane

CH3 CH2 CH CH2 CH2 CH CH2 CH3

CH3 CH2 CH3

Which end do we number from?Which end do we number from?

8 7 6 5 4 3 2 1

3-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).

OR7-(1,1-dimethylethyl)-4-(1-methylethyl)-8-(2-methylpropyl)dodecane

Name the following compounds.

CH2CH2

CH2CH

CH2CH3 C

CH2CH2

CH2CH2

CH2CH3

CH3

CCH3 CH2

CH3 CH2 CH3

CH3

Good Luck!Good Luck!

7-(1,1-Dimethylbutyl)-3-ethyl-7-methyldodecane

Branched Substituents

isopropyl

sec-butyl

CH3 CH CH2

CH3

CH2 CH

CH3

CH3 CH3 C CH3

CH3

CH3 CH CH3

isobutyl tert-butyl(t-butyl)

CH3 C CH3

CH2

CH3

neo-pentyl

Halogens and other side groups Fluoro –F Chloro –Cl Bromo –Br Iodo –I Nitro –NO2 N

O

O

CH3 CH2 Br

Bromoethane

“Ethyl bromide”

CH3 C Cl

CH3

CH3

2-Chloro-2-methylpropane

“tert-Butyl chloride”

CH3 CH CH CH2 CH3

Br CH3

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.1

2

31-methyl-3-(1,2-dimethylpropyl)cyclohexane =>

The isopropyl group can be named The isopropyl group can be named as a “complex” substituentas a “complex” substituent

1-methylethyl

CH3 CH

CH3

2 1

If you can name this,If you can name this,you can name almost anything!you can name almost anything!

1 2 3 4 5 6

7

8 9

4-isopropyl-2,6,6-trimethylnonane

CH3 CH CH2 CH CH2 C CH3

CH3

CH

CH3

CH3

CH3

CH2

CH2 CH3

Now, rename the isopropyl group. Now, rename the isopropyl group. Notice the alphabetical order!Notice the alphabetical order!

1 2 3 4 5 6

7

8 9

2,6,6-trimethyl-4-(1-methylethyl)nonane

CH3 CH CH2 CH CH2 C CH3

CH3

CH

CH3

CH3

CH3

CH2

CH2 CH3

Naming complex substituents -- Naming complex substituents -- this one is alphabetized under dthis one is alphabetized under d

1,3-dimethylbutyl

CH3 CH CH2 CH

CH3CH3

4 3 2 1

deciding on alphabetical order deciding on alphabetical order for complex groupsfor 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 substituentsNaming complex substituents

2-ethyl-1,1-dimethylbutyl

CH3 C CH CH2 CH3

CH3 CH2 CH3

1 2 3 4

CH3 CH2 CH2 CH2 C CH2 CH2 CH2 CH3

C

CH2 CH2 CH3

CH3

CH2CH2 CH3CH3

This Should Be FunThis Should Be Fun

1 2 3

1 2 3 4 5 6 7 8 9

5-(1-Ethyl-1-methylpropyl)-5-propylnonane

CH2CH2

CH2CH

CH2CH3 C

CH2CH2

CH3

CH2CH3

CH3

CCH3 CH3

CH3

name this two ways -- name this two ways -- (the complex group)(the complex group)

7-(1,1-dimethylethyl)-3-ethyl-7-methyldecane7-tert-butyl-3-ethyl-7-methyldecane

Common Nomenclature Common Nomenclature PitfallsPitfalls

Did not find the longest carbon chainNumbered chain from the wrong endForgot 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 wordIncorrect punctuation

degree of substitutiondegree of substitutionCH3 R R CH2 R

R CH R

R

R C R

R

R

primary (1°) secondary (2°)

tertiary (3°) quaternary (4°)

CH3 CH CH2 CH CH2 C CH3

CH3

CH

CH3

CH3

CH3

CH2

CH2 CH3

Degree of SubstitutionDegree of Substitution

1° 1°

1° 3° 2° 3° 2° 4° 1°

1° 3° 2°

1° 2° 1°

LOCANT PREFIX N STEM SUFFIX

numbers substituents number -ALK(AN)- ending

Block diagram for Block diagram for nomenclaturenomenclature

cyclic moleculescyclic molecules

CC

C

H H

H

H

H

H

CH2

CH2

CH2

Cyclopropane

C

C C

C

H

H

H

H

H

H

H

H

CH2

CH2 CH2

CH2

Cyclobutane

C

CC

C

C

H HH H

HH

HH

HHCH2

CH2

CH2

CH2

CH2

Cyclopentane

C

CC

C

CC

H HH

H

H

H

HH

H

H

H

HCH2

CH2CH2

CH2

CH2

CH2

Cyclohexane

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 Nomenclature of the Substituted CycloalkanesCycloalkanes

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.

Br

Bromocyclopropane

CH3

CH3

1,1-Dimethylcyclohexane

CH3

CH3

CH2CH3

4-Ethyl-1,1-dimethylcyclohexane

Two ways of naming thisTwo ways of naming this

1-isopropyl-2-methylcyclohexane1-methyl-2-(1-methylethyl)cyclohexane

CH3

CH

CH3

CH3

Numbering Starts at the Most Numbering Starts at the Most Highly-Substituted CarbonHighly-Substituted Carbon

Cl CH3

CH3

CH3

2 13 74 6 5

2-Chloro-1,1,6-trimethylcycloheptane

cycloalkyl groupscycloalkyl groups

Cyclopropyl Cyclobutyl

Cyclopentyl Cyclohexyl

C

CH3

CH2CH2CH3 CH3

3-Cyclobutyl-3-methylpentane

CH3 CH2 CH CH3

2-Cyclobutylbutanesec-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