ORGANIC CHEMISTRY Classes of Organic Compounds. Classification of Hydrocarbons 1. Aromatic Hydrocarbons-contain one or more benzene rings 2. Aliphatic.
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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.
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.
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
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
Optical Isomers
Optical Isomerism (Chiralty) occurs when there is an asymmetric carbon (C has 4 different atoms or groups attached)
Chirality is important in drugs and enzyme-catalyyzed rxns. Only L-form of ascorbic acid functions as vitamin C.
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
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.
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.
AROMATIC HYDROCARBONSContain Benzene ringMost have distinctive odors.Thousands of compounds are derived from benzene.
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