Islamic University of Gaza Organic chemistry A Chapter 3 Alkanes By Prof. Dr. Adel M. Awadallah Islamic University of Gaza

Alkanes and Cycloalkanes Hydrocarbons (contain only carbon and hydrogen) Saturated: (Contain only single bonds) Alkanes (CnH2N + 2 ) Cycloalkanes (CnH2N ) b) Unsaturated: contain Alkenes: double bonds (,,,CnH2N) Alkynes: triple bonds ((CnH2N - 2) Aromatic: benzene like compounds

The structure of alkanes

Alkyl groups

Nomenclature of substituted alkanes Choose the largest continuous chain Start numbering (lowest possible numbering) List substituents alphabitically. Use di, tri, tetra, penta, hexa, hepta, octa, nona, deca for identical groups Examples

If there are two equally long continuous chains, choose the one with most branches

Conformations of Alkanes: Conformers: Stereoisomers that are interconvertible by bond rotation

Potential Energy Changes in Ethane

Propane and Butane

Conformations of n-butane

Pentane and Hexane

Classes of carbon atoms and hydrogen atoms

Physical properties of alkanes 1) Water insoluble 2) low boiling point, which increases upon increasing the number of carbons in the alkane 3) branched alkanes have lower boiling points than the corresponding long chain alkanes

Industrial Sources

Preparation of Alkanes

Examples

Orientation of Halogenation

Ease of Abstraction of Hydrogen atoms

Transition State forHalogenation Factors that tend to stabilize the free radical tend to stabilize the incipient free radical in the transition state

Non-rearrangement of free radical