Isomers For each of the following: 1 Name the compounds shown. 2 Identify the structural isomers. 3 Identify the geometric isomers.

butane propene methylpropane ethene but-1-ene methylpropene cis but-2-ene trans but-2-ene

IUPAC name = Alkanols CnH2n+1OH for saturated acohols Can be written R-OH Alcohols with three or more carbons form structural isomers.

Alcohols

Alcohols

Naming and Structure -ol replaces the –e Parent chain contains –OH Position of hydroxyl group determines numbering of alkyl groups (i.e count from the lowest carbon chain) Prefix –di, -tri indicate multiple functional groups

H H H H H – C – C – C – C – OH H CH3 H H Butane H H H H H – C – C – C – C – OH H CH3 H H Butan-1-ol H H H H H – C – C – C – C – OH H CH3 H H 3-methylbutane-1-ol

Properties Hydrogen bonding due to –OH groups creating polarity Determines physical properties for smaller molecules Permanent dipoles and instantaneous dipoles Non-polar hydrocarbon portion determines properties for larger molecules

Melting & Boiling Points pH & Conduction Non-conductors Neutral solutions Melting & Boiling Points Higher than corresponding alkane due to hydrogen bonding Liquids at room temp up to 8Carbons

Solubility Up to 3 Carbon soluble in very water 4 Carbon soluble in water 5-6 Carbon slightly soluble Solubility due to polarity >6 C insoluble in water due to large non-polar alkyl (hydrocarbon) region. Commercial solvent as they can dissolve both polar and non-polar substances.

1,2-Ethanediol Two hydroxyl groups = greater hydrogen bonding Antifreeze Antiboil De-icing fluid

Alcohols II Isomerism

Cis-trans isomers Which of the following compounds will have cis-trans isomers? (Hint: Draw the structure.) 1 CHCl=CH2 2 CH3CH=CHCH2CH3 3 CHCl=CHCl 4 CH2=CBr2 5 CHBr=CBrCH3 The following have cis-trans isomers 2 CH3CH=CHCH2CH3 CHCl=CHCl 5 CHBr=CBrCH3

Structural Isomerism H H H H – C – C – C – OH H CH3 H methylpropan-1-ol H H H H H – C – C – C – C – OH H H H H butan-1-ol

Primary, secondary, tertiary Determined by number of alkyl groups attached to the same carbon as -OH Distinguished by Lucas reagent (ZnCl2 in conc HCl) no visible reaction: primary alcohol solution turns cloudy in 3-5 minutes: secondary alcohol solution turns cloudy immediately, and/or phases separate: tertiary or benzyl alcohol

Primary alcohols are those alcohols in which the carbon atom to which the hydroxyl group ( OH) is attached has only one carbon attached to it. (usually at the end of the chain) I.e. the carbon with OH group is bonded to only one other carbon atom. E.g.

Secondary alcohols are those alcohols in which the carbon atom to which the hydroxyl group ( OH) is attached has two carbons attached to it E.g. Butan-2-ol

Tertiary alcohols

Tertiary alcohols are those alcohols in which the carbon atom to which the hydroxyl group ( OH) is attached has three carbons attached to it

Optical Isomers A form of stereoisomerism In stereoisomerism, the atoms making up the isomers are joined up in the same order, but still manage to have a different spatial arrangement. Why optical isomers? Optical isomers are named like this because of their effect on plane polarised light. Simple substances which show optical isomerism exist as two isomers known as enantiomers.

Butan-2-ol