Aromatic Hydrocarbons Aromatic structures are formally related to benzene. The delocalized  electrons are usually represented as a circle in the center of the ring. Benzene is a planar symmetrical molecule. Benzene is not reactive because of the stability associated with the delocalized  electrons. Most aromatic rings are given common names.

Even though they contain  bonds, aromatic hydrocarbons undergo substitution more readily than addition (because of delocalization of  bonds). Example: if benzene is treated with nitric acid in the presence of sulfuric acid (catalyst), nitrobenzene is produced.

Functional Groups To get reactivity out of an organic molecule, functional groups have to be added. Functional groups control how a molecule functions. More complicated functional groups contain elements other than C or H (heteroatoms). Functional group containing molecules can either be saturated (alcohols, ethers, amines etc.) or unsaturated (carboxylic acids, esters, amides, etc.). We usually use R to represent alkyl groups (hydrocarbon).

Alcohols (alkanols) (R-OH) Alcohols are derived from hydrocarbons and contain -OH groups. The names are derived from the hydrocarbon name with -ol replacing the e at the end of the -ane suffix. Example: ethane becomes ethanol. Since the O-H bond is polar, alcohols are more water soluble than alkanes. CH3OH, methanol, is used as a gasoline additive and a fuel. Polyhydroxy alcohols (polyols) contain more than one OH group per molecule (e.g. ethane-1,2-diol - ethylene glycol used as antifreeze).

Primary Alcohol – The C on which the OH is attached has only one other C atom directly attached to it. Secondary Alcohol – The C on which the OH is attached has 2 other C atoms directly attached to it. Tertiary Alcohol – The C on which the OH is attached has 3 other C atoms directly attached to it.

Naming Alcohols – Name like alkanes (count carbon atoms, attach substituents), replace “e” with “ol.” = ethanol

Propan-2-ol 2-methylpropan-2-ol Ethan-1,2-diol propan-1,2,3-triol

Reactions of Alcohols 1. Complete combustion: C2H5OH + O2  CO2 + H2O 2. Oxidation – warmed with acidified potassium dichromate (Cr2O72-) Primary alcohols oxidized to aldehydes, then to carboxylic acids. To maximize aldehyde production, the product is distilled as it is formed. To maximize carboxylic acid production, the products are heated under reflux for long periods.

Secondary alcohols (C with OH is attached to 2 other C) oxidized to ketones Tertiary alcohols (C with OH is attached to 3 other C – no H atoms attached to C with OH) cannot be oxidized by dichromate

Dehydration (in concentrated sulfuric or phosphoric acid) – produces a double bond (opposite of addition of water)

Ethers (R-O-R′) Compounds in which two hydrocarbons linked by an oxygen are called ethers. Ethers are commonly used as solvents. = ethoxyethane or diethyl ether

Compounds with a Carbonyl Group Aldehydes and Ketones The carbonyl functional group is C=O. Aldehydes (alkanals) must have at least one H atom attached to the carbonyl group: Ketones (alkanones) must have two C atoms attached to the carbonyl group: Aldehydes and ketones are prepared from the oxidation of alcohols.

Named as alkanes with “-al” (aldehydes) or “-one” (ketones) added to the end. The carbon on which the oxygen is attached is numbered. Examples 1. propanone 2. ethanal 3. heptan-3-one