Alkanes, Alkenes and Alkynes

SCH4U Spring 2012

Single covalent bonds Saturated hydrocarbons Nonpolar Not soluble in water Soluble in benzene and other non-polar

solvents General formula: CnH2n+2 (n represents the

number of carbon atoms)

Alkanes

Alkanes- Examples

e.g. C4H10

Empirical molecular formula C4H10 Expanded molecular formula CH3CH2CH2CH3 Structural formula

Condensed structural formula CH3-CH2-CH2-CH3 Line structural formula

Ways to represent structures

Three basic parts:

Root: denotes the number of carbon atoms in the longest continuous chain of carbon atoms

Prefix: gives the positions and names of any branches from the main chain

Suffix: indicates the series to which the molecule belongs (e.g. –ane)

IUPAC name of organic compounds

Root and side group names

Identify the root Identify the longest continuous chain Find the root for the number of carbons in the chain

Identify the suffix

Identify the prefix Identify the number of carbon atoms in each side group and determine the name If there is more than one type of side group, write their names in alphabetical

order Find the position of each side group. Numbering must begin at the end of the

main chain that will give the side groups the lowest possible numbers Use a hyphen to separate numbers and words and use a comma to separate the

numbers Use a prefix to indicate how many of each type of side group are present if there

is more than one of the same side group (e.g. di-, tri-, tetra-)

Name the compound

Naming Alkanes

Name the following molecules

Questions

Identify the root Identify the suffix Draw and number the main chain, but do

not add any hydrogen atoms yet Identify the prefix and draw the side groups Add hydrogen atoms

Drawing Alkanes

Draw the condensed formula for • 2-methylbutane• 2,2-dimethyl-3-propyloctane

Draw the line structural formula for• 3,3,4-triethylnonane• 3,3,4,4-tetramethyldecane

Questions

Small alkanes are gases at standard temperature

Medium-length alkanes are liquids at standard temperature

Very large alkanes are waxy solids The larger the alkane, the higher the boiling

point

Physical properties of alkanes

At least one double bond in the carbon chain

At least two carbon atoms Unsaturated hydrocarbons Non-polar Do not dissolve in water General formula (one double bond): CnH2n

Alkenes

Identify the root• Identify the longest continuous chain that contains the double bond• Find the root for the number of carbons in the chain

Identify the suffix• Number the main chain by starting at the end of the chain nearest

the double bond• If the alkene contains four or more carbons, give the position of the

double bond by indicating the number of the carbon atom that precedes the double bond. The suffix consists of a hyphen, the number and -ene

Identify the prefix

Name the compound

Naming Alkenes

Name each alkene

Questions

Draw the condensed structural formula for• 3-propylhept-2-ene• 4-ethyl-2,5-dimethyloct-3-ene

Draw a line structural formula for• 2-methylbut-1-ene• 4-ethyl-4,5-dimethylhex-1-ene

Questions

The first three alkenes are all gases at standard temperature

Intermediate size alkenes are liquids Boiling points of the alkenes are slightly

lower than those of the alkanes that have the same number of carbon atoms

Physical properties of alkenes

At least one triple bond Unsaturated hydrocarbons non-polar Insoluble in water General formula: CnH2n-2

Alkynes

Draw the condensed structural formula for:• But-2-yne• 4-ethyl-4-methylhept-2-yne

Draw a line structural formula for • 4,5-dimethylhex-1-yne• 2,5,7-trimethylnon-3-yne

Questions

First few alkynes exist as gases at standard temperature

Higher boiling point than the corresponding alkanes

Physical properties of alkynes