Organic Chemistry

- Alkenes / Dienes- Alkynes

Alkenes The Alkenes form another homologous

hydrocarbon series

Each member contains one double covalent bond between two C atoms. So alkenes are said to be unsaturated. Only 3 atoms joined to each C, not 4

General formula = CnH2n What was the general formula for the Alkanes?

Saturated vs Unsaturated

Saturation vs. Unsaturation Simply put, a saturated

hydrocarbon has no double bonds between the Carbon atoms (ex. alkanes)

Unsaturated has one or more double or triple bonds between carbons (alkenes, alkynes)

CC C

C

H

H

H

H

HH

H

H

H

H

CH3(CH2)2CH3

CH

CH3 CH

CH3

CH3C C

CH3

Physical properties of the Alkenes

- Very similar to the alkanes

- Insoluble in water- very soluble in organic solvents

- Less dense than water

- B.P. and M.P increase with increasing carbon- As with alkanes B.P rises about 20-30 C per carbon- Hexane b.p. 69 C; 1-Hexene b.p. 63.5 C- Heptane b.p. 98 C; 1-Heptene b.p. 93 C

Naming Alkenes Names are derived from the name of the alkane

chain with the same number of C atoms.

Replace the –ane ending of the alkane name with –ene.

1st member is C2H4, ethene.H H

C=C H H

Alkene Homologous Series(C1-C2 double bond)

Ethene Propene 1-Butene 1-Pentene 1-Hexene 1-Heptene 1-Octene 1-Nonene 1-Decene

C=CC-C=CC-C-C=CC-C-C-C=CC-C-C-C-C=CC-C-C-C-C-C=CC-C-C-C-C-C-C=CC-C-C-C-C-C-C-C=CC-C-C-C-C-C-C-C-C=C

Naming Alkenes Location of double bond is specified by

numbering C atoms in backbone. Give bond the lowest possible number.

H H H C=C–C–C–HH H H H

C4H8

CH2CHCH2CH3

H H H HH–C–C=C–C–H H H

C4H8

CH3CHCHCH3

1-butene (not 4) 2-butene

Structural Formula

Chemical formula

CondensedStructural formula

Naming Alkenes Once double bond is numbered specify

substituents alphabetically by number

Use di, tri and tetra for multiple substituents of the same group

C=C–C–C C C

C6H12

CH2C(CH3)CH(CH3)CH3

Structural Formula(w/o the H)

Chemical formula

CondensedStructural formula

2,3-dimethyl-1-butene

Problems: Draw the following

alkenes:

2-Butene 2–methylpropene 4–Methyl–2-pentene 3,3-Dimethyl-1-butene

Name this Compound:

4-ethyl-5-methyl-4-octene

Dienes Alkenes = 1 double

bond Dienes have 2

double bonds End in -diene Location still

denoted by numbers

Determine which way to number the C backbone by assigning the lowest possible number to one of the double bonds

Example: 1,3 – pentadienec=c-c=c-cNot 2,4-pentadiene

Substituents are named first

[Numbers are separated by commas and the #’s are

Separated from the name by a dash

Double bonds must all be in the backbone.

Name this compound:

C=C-C-C-C=C-C C

5-methyl-1,5-heptadiene

Draw 2-methyl-1,3-heptadiene:

C=C-C=C-C-C-C C

Alkynes Homologous series of unsaturated

hydrocarbons that contain one triple bond.

Each member contains one triple carbon-carbon bond.

Alkynes are unsaturated.

General formula = CnH2n-2

Alkyne Homologous Series(C1-C2 triple bond)

Ethyne Propyne 1-Butyne 1-Pentyne 1-Hexyne 1-Heptyne 1-Octyne 1-Nonyne 1-Decyne

C CC-C CC-C-C CC-C-C-C CC-C-C-C-C CC-C-C-C-C-C CC-C-C-C-C-C-C CC-C-C-C-C-C-C-C CC-C-C-C-C-C-C-C-C C

Ethene

(Common name)

A common use of one of the alkynes:The Acetylene torch

Hydrocarbon Table

Notice that eachOf the hydrocarbonFamilies differsFrom the next By 2 hydrogen

Alkanes share 1pr e-

Alkenes share 2pr e-

Alkynes share 3pr e-

Can you explain howThe above commentsAre related?

Naming Alkynes Use the corresponding name from the alkane

series and change the –ane to –yne.

If necessary, number the carbon atom at which the triple bond occurs with the lowest number.

Use the same naming process you used for naming Alkenes

H–CC–H C2H2 ethyne CHCH

HH–CC–C–H C3H4 propyne CHCCH3

H

H HH–CC–C–C–H C4H6 1-butyne CHCCH2CH3

H H

H HH–C–CC–C–H C4H6 2-butyne CH3CCCH3

H H

Structural Chemical Name CondensedFormula Formula Structural formula

Can you name this compound?

3-ethyl-1-pentyne