Unsaturated Hydrocarbons

Transcription

1 Unsaturated ydrocarbons

2 hemical Formulas and Unsaturation n n 2n n 2n+2 n 2n+2

3 hemical Formulas and Unsaturation n n n n 2n n 2n

4 hemical Formulas and Unsaturation ydrocarbons Saturated ydrocarbons Unsaturated ydrocarbons Alkanes n2n+2 ycloalkanes n2n (one ring) Alkenes n2n (one =) Alkynes n2n-2 (one ) Benzene 66 n2n-6

5 Review of arbon Bonding Patterns

6 lasses of Unsaturated ydrocarbons 120º 180º 120º

7 Lewis Representation of Ethene Note: Both of these representations picture the two components of the double bond as being identical. This is not the case.

8 ovalent Bonding in Ethene The two carbons and all four hydrogens all lie within the same plane. The bond angles are all 120º. Note: Though the two components of the double bond are pictured the same, one of the bonds is actually weaker than the other.

9 Supplement on ybridization in Ethene

10 ybrid Orbitals - Bonding in Methane Recall that the four orbitals associated with the bonding in an alkane or cycloalkane are the result of sp 3 hybridizaton.

11 ybrid Orbitals - Alkenes The four orbitals associated with the bonding in alkenes or cycloalkenes are the result of sp 2 hybridizaton.

12 ovalent Bonding in Ethene 24, ethene, is formed from two sp 2 hybridized carbon atoms and four hydrogen atoms: Lateral overlap of the unhybridized p orbitals, above and below the triangular planes, results in a π bond of the double bond.

13 Nomenclature of Alkenes 1. Select the longest carbon chain containing the double bond as the parent chain. Replace the -ane ending with -ene. 2. Number the parent chain beginning at end closest to the double bond beginning with the first carbon in the chain. 3. Locate and name the substituents in alphabetical order. 4. ompounds with two double bonds are called dienes. 5. yclic compounds are named as cycloalkenes. arbons in the double bond are always numbered first. Then the ring is numbered in the direction so as to give the lowest numbers to substituents.

14 Positional Isomerism Isomerism in Alkenes pentene 2-pentene???? also 2-pentene Geometric Isomerism (a form of stereoisomerism)

15 Alkenes-Nomenclature

16 Alkenes-Nomenclature 2-hexene 2-methyl-3-hexene

17 Alkenes-Nomenclature Practice 2,3-dimethyl-1-pentene 2,3-dimethyl-2-hexene

18 Alkenes-Nomenclature 4-methylcyclohexene

19 Alkenes-Nomenclature Practice 2,5-dimethyl-2-heptene 3,3-dimethylcyclopentene

20 Exercises on Alkene Nomenclature

21 1 a) b) c) l 3 2 3

22 Geometric Isomerism (a form of stereoisomerism) Isomerism in Alkenes Exists for the following cases: X Y A B A B and E D X Y A B Y X A B A result of lack of free rotation around the double bond X E D E D D E

23 Isomerism in Alkenes

24 Isomerism in Alkenes is/trans isomers have different physical properties

25 Isomerism in Alkenes is/trans isomers are not possible for some alkenes.

26 Alkenes-Nomenclature Practice cis-4-methyl-2-hexene trans-5,6-dimethyl-3-heptene

27 2 a) cis-1-chloro-1-butene l 2 3 b) trans-3-hexene c) trans-4,4-dimethyl-2-pentene d) cis-1,3-dichlorocyclohexane l l

28 Alkynes

29 Supplement on ybridization in Ethyne

30 Alkynes Structure of the Triple Bond Note: Both of these representations picture the three components of the triple bond as being identical. This is not the case.

31 Ethane, 33 The sp 3 hybrid orbitals of two carbons overlap The remaining sp 3 hybrid orbitals overlap with hydrogen s orbitals 7 sigma bonds

32 Ethene, 22 The sp 2 hybrid orbitals of two carbons overlap The remaining sp 2 hybrid orbitals overlap with hydrogen s orbitals 5 sigma bonds

33 Ethene, 22 The remaining unhybridized p orbitals overlap to form a bond. 5 sigma bonds and 1 bond

34 Ethyne, The sp hybrid orbitals of two carbons overlap The remaining sp hybrid orbitals overlap with hydrogen s orbitals 3 sigma bonds

35 Ethyne, The remaining unhybridized p orbitals overlap to form 2 bonds. 3 sigma bonds and 2 bonds

36 Bonding in

37 Summary of ydrocarbon Bonding

38 Alkynes Structure of the Triple Bond Note: Both of these representations picture the three components of the triple bond as being identical. This is not the case.

39 Nomenclature of Alkynes 1. Select the longest carbon chain containing the triple bond as the parent chain. Replace the -ane ending with -yne. 2. Number the parent chain beginning at end closest to the triple bond beginning with the first carbon in the chain. 3. Locate and name the substituents in alphabetical order.

40 Alkynes-Nomenclature Practice 4,4-dimethyl-1-hexyne 2,7-dimethyl-4-octyne

41 Alkynes-Nomenclature Practice l l

42 Properties of Alkenes and Alkynes Nonpolar and insoluble in water as are alkanes. Nonpolar, therefore Boiling points depend on size and shape. Flammable. Alkenes may display cis-trans isomerism. hemically reactive at the multiple bond.