CHEM1201 Lecture Notes - Lecture 15: Stereocenter, Stereoisomerism, Structural Isomer

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Alkenes:

- Aliphatic, unsaturated hydrocarbons

o C=C double bonds

- Formula for one double bond in noncyclic compound: CnH2n

o Subtract 2H from alkane for each double bond

- Polyunsaturated – many double bonds

- Trigonal planar geometry around C

o Flat

- E.g. ethene or ethylene

Alkynes:

- Aliphatic, unsaturated hydrocarbons

o CC triple bond

- Formula of compound with one triple bond is CnH2n-2

- Linear geometry

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Naming alkenes and alkynes:

*same way as alkanes except

- the base chain is the longest continuous carbon chain that contains the double or

triple bond

- the base name ends in –ene for alkenes and –yne for alkynes

- number the chain from the end closest to the multiple bond

- the number in front of the main name indicates the first carbon of the multiple bond

Examples:

a) 3,4-dimethyl-3-hexene b) 3-isopropyl-4-methyl-1-pentyne

a) 4-methyl-2-pentene b) 3-ethyl-3-methyl-1-pentyne

Functional groups:

- functional groups are specific groups (moieties) of atoms or bonds within molecules

that are responsible for the characteristic chemical reactions of those molecules

- double bonds are more reactive than single bonds

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Related Questions

Hydrocarbons are organic molecules that solely consist of hydrogen and carbon atoms. These compounds are considered saturated if they contain the maximum number of hydrogen atoms. Degrees of unsaturation are structural features that cause a compound to have less than the maximum number of hydrogen atoms possible, and cause the hydrocarbon to be considered unsaturated. In hydrocarbons, degrees of unsaturation consist of ring structures and pi bonds (double and triple bonds). The following formulas can be used to determine whether a molecular formula represents an alkane, alkene, or alkyne (assuming that the hydrocarbons are not ring structures, and that the unsaturated compounds only have one double or triple bond).

Alkanes: CnH2n+2

Alkenes: CnH2n

Alkynes: CnH2nâ2

Classify each of the following statements as true or false:

a) To be classified as organic, a compound must be or have been part of a living organism.

b) Carbon atoms normally form four bonds in organic compounds.

c) Only an unsaturated hydrocarbon can engage in an addition reaction.

d) Members of a homologous series differ by a distinct structural unit.

e) Alkanes, alkenes, and alkynes are unsaturated hydrocarbons.

f) Alkyl groups are a class of organic compounds.

g) Isomers have the same molecular formulas but different structural formulas.

h) Cis-trans isomerism appear among alkenes but not alkynes.

i) All aliphatic hydrocarbons are unsaturated.

j) Aromatic hydrocarbons have a ring structure.

k) An alcohol has an alkyl group bonded to an oxygen atom, and an ether has two.

l) Carbonyl groups are found in alcohols and aldehydes.

m) An ester is an aromatic carbon made from the reaction of an alcohol and a carboxylic acid.

n) An amine has one, two, or three alkyl groups substituted for hydrogens in an ammonia molecule.

o) An amide has the structure of a carboxylic acid except that replaces OH in the carboxyl group.

p) A peptide linkage series arises when a water molecule forms from a hydrogen from the of one amino acid molecule an from an another amino acid molecule.