ORGANIC CHEMISTRYClasses of Organic Compounds

Classification of Hydrocarbons1. Aromatic Hydrocarbons-contain one or more benzene rings

2. Aliphatic Hydrocarbons - all other hydrocarbons

Aliphatic Hydrocarbons

Carbon atoms can be bonded in straight chains, branched chains, or rings.Chains may contain single, double, or triple bonds.A saturated compound contains only single bond between carbons. These are alkanes.

ALKANES

Simplest hydrocarbonEach differs from the next by a -CH2- group.Compounds whose structures differ from each other by a specific structural unit is called a homologous series.

ALKANES

Simplest alkane is methane. CH4General formula of alkane is CnH2n+2All end in -aneSoluble in nonpolar solvents,C to C bonds have sp3 hybridization.

Hydrocarbon Prefixes

ALKANES

When a hydrogen along with its associated electrons is removed from a hydrocarbon molecule, a radical is left.CH3 is a radical. It is named methyl.Radicals end in -yl.Alkanes form alkyl groups.

Branched Chain Alkanes1. Find longest continuous chain or parent chain.2. Add the name of the branches (substituents) attached in alphabetical order using prefixes.3. Number Carbon atoms in parent4. Insert position # of each substituent group5. Punctuate name - separate position # with hyphens, more than one # is separated by commas.

Cycloalkanes

Alkane ringsGeneral formula is CnH2nExample cyclopentane C5H10

Isomers

Isomerism is the existence of two or more substances with the same molecular formula, but different molecular structures.Important because structure determines properties and function.There are two main types of isomers.

Structural Isomers

Structural Isomers

Also called constitutional isomers.Atoms are bonded in different arrangements--thus different properties.

Longer chains have higher boiling points (BP) and melting points (MP)Having branches on the chain serves to lower the BP but it raises the melting point.

Stereoisomers

All atoms are bonded in the same order but are arranged differently in space.There are two types:

a. Geometric isomersb. Optical isomers

Geometric Isomers

Structural isomers have a different arrangement of groups around a double bond.In alkenes with double bonds, the carbon is locked in place and cannot rotate freely as it could in alkanes with single bonds. Pi bonds

Geometric isomers

Optical Isomers

Optical Isomerism (Chiralty) occurs when there is an asymmetric carbon (C has 4 different atoms or groups attached)

Chiral Molecules

Chirality is important in drugs and enzyme-catalyyzed rxns. Only L-form of ascorbic acid functions as vitamin C.

Geometric Isomers

Properties and Uses of Alkanes1. C-H bonds are nonpolar2. Strength of London dispersion forces increases as mass increases--# of C determines state of matter.3. Longer the chain, higher the boiling point.

Properties and uses of alkanes4. Alkanes less reactive than other hydrocarbons due to stability of single covalent bonds.

5. Most important rxn is combustion.

Fractional DistillationGasoline is a component of fossil fuel. Is can be extracted by fractional distillation.

Combustion

Straight-chain alkanes ignite more spontaneously than branched chains but cause knocking in autos.Octane rating is a measure of burning efficiency and antiknock properties.2,2,4-trimethyl pentane (isooctane) resists knocking

C8H18

2,2,4-trimethylpentane octane

Unsaturated Hydrocarbons

Contain double and triple carbon to carbon bonds.Include Alkenes and Alkynes

ALKENES

Olefin is another name.Contain double bonds.General formula CnH2nDouble bond is shorter than a single bond and it is also stronger and more reactive.Double C bonds have sp2 hybridization.

Naming Alkenes

End in -ene.The double bond location takes precedence in naming.If there is more than one double bond, the location is numbered and a prefix is used 2 = adiene 3 = atriene

Alkenes are numbered so that the lowest position number is assigned to the first carbon atom to which the double bond is attached.

1,4-pentadiene

Ethene

#1 organic chemical in industryProduct of petroleum refiningMakes plastics andsynthetics

ALKYNES

Contain triple bonds.General formula is CnH2n-2End in -yne Ethyne or acetylene

Naming Alkynes

The numbering system follows the same pattern used for naming alkenes. 4,4-dimethyl-2-pentyne

If a compound has both double and triple bonds, the double bonds take precedencein numbering.The double bond is given the lowest number and named first.

Benzene Ring

Kekule’s snake

AROMATIC HYDROCARBONSContain Benzene ringMost have distinctive odors.Thousands of compounds are derived from benzene.

Ways to diagram benzeneImportant in making plastics and fibers

Naphthalene

2 benzene rings

Phenyl Radical

Methyl Benzene or Tolueneimproves quality of gasolineused in production of explosives TNT

Functional Groups

A substituent group that is not made up of only carbon and hydrogen is a functional group. -OH is hydroxide