Alkenes Alkynes Mr Shields Regents Chemistry U 16

- Alkenes - Alkynes Mr. Shields Regents Chemistry U 16 L 03 1

Alkenes Ø Like the alkanes, the Alkenes form another homologous hydrocarbon series Ø Each member contains one double covalent bond between two C atoms. l So alkenes are unsaturated hydrocarbons. Ø General formula = Cn. H 2 n (2 H less than the Alkanes) l What was the general formula for the Alkanes? 2

Saturated vs Unsaturated 3

Saturation vs. Unsaturation Ø Simply put, a saturated hydrocarbon has no double bonds between the Carbon atoms (ex. alkanes) Ø Unsaturated has one or more double or triple bonds between carbons (alkenes, alkynes) 4

Physical properties of the Alkenes -Alkenes have properties similar to the alkanes - Insoluble in water - But very soluble in organic solvents - Less dense than water (density of water = 1. 0) - B. P. and M. P increase w/ increasing carbon # - Slightly lower than the corresponding alkane - 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 5

Naming Alkenes Ø Names are derived using the same prefix used to name the alkane chain with the same number of C atoms. Ø Replace the –ane ending of the alkane name with –ene. 1 st member is C 2 H 4, ethene. H H Why 1 st ? C=C H H 6

Naming Alkenes Ø Location of double bond is specified by numbering C atoms in longest C backbone. Give double bond the lowest possible number. l Do not use a # if there is only 1 possible location 1 -butene (not 3) H HH C=C–C–C–H H H 2 -butene H H HH H–C–C=C–C–H H H Structural Formula C 4 H 8 Chemical formula CH 2 CH 3 CHCHCH 3 Condensed Structural formula 7

Alkene Homologous Series (w/ C 1 -C 2 double bond) Ethene Ø Propene Ø 1 -Butene Ø 1 -Pentene Ø 1 -Hexene Ø 1 -Heptene Ø 1 -Octene Ø 1 -Nonene Ø 1 -Decene Ø C=C C-C-C=C C-C-C-C-C=C C-C-C-C-C-C-C=C What is the name of this alkene? C-C-C=C-C-C-C 8

Naming Alkenes Ø Once double bond is numbered specify substituents alphabetically by carbon number l Do not use a number if there is only 1 possible location Ø Use di, tri and tetra for multiple substituents of the same group 2, 3 -dimethyl-1 -butene C=C–C–C C C Structural Formula (w/o the H) C 6 H 12 Chemical formula CH 2 C(CH 3)CH 3 Condensed Structural formula 9

Problems: Ø Draw the following alkenes: l l 2 -Butene methylpropene 4–Methyl– 2 -pentene 3, 3 -Dimethyl-1 -butene 10

Name this Compound: And “E” before “M” 4 -ethyl-5 -methyl-4 -octene (why? What is the longest C chain? 11

Alkynes Ø Homologous series of unsaturated hydrocarbons that contain one triple bond. Ø Each member contains one triple carbon-carbon bond. l Ø Alkynes are unsaturated. General formula = Cn. H 2 n-2 12

Alkyne Homologous Series (w/ C 1 -C 2 triple bond) Ethyne Ø Propyne Ø 1 -Butyne Ø 1 -Pentyne Ø 1 -Hexyne Ø 1 -Heptyne Ø 1 -Octyne Ø 1 -Nonyne Ø 1 -Decyne Ø C C C-C-C-C-C C C-C-C-C-C-C-C C 13

Ethyne (Common name) A common use of one of the alkynes: The Acetylene torch What is the IUPAC name for this compound? 14

Hydrocarbon Table Notice that each Of the hydrocarbon Families differs From the next By 2 hydrogen Alkanes share 1 pr e. Alkenes share 2 pr e. Alkynes share 3 pr e- 15

Naming Alkynes Ø Use the corresponding name from the alkane series and change the –ane to –yne. Ø If necessary, number the carbon atom at which the triple bond occurs with the lowest number. Ø Use the same naming process you used for naming Alkenes 16

Structural Formula Chemical Formula Name Condensed Structural formula H–C C–H C 2 H 2 ethyne CHCH H H–C C–C–H H C 3 H 4 propyne CHCCH 3 HH H–C C–C–C–H HH C 4 H 6 1 -butyne CHCCH 2 CH 3 H H H–C–C C–C–H H H C 4 H 6 2 -butyne CH 3 CCCH 3 17

Can you name this compound? 3 -ethyl-1 -pentyne 18

Problems Name this alkyne: C C-C-C=C-C-C C C C 5, 7 -diethyl-3 -methyl-4 -decyne 19