Alkanes C H n 2n+2 all C are sp3 hybridized 4  bonds 109.5o n root suffix formula 3 prop ane C3H8 4 but ane C4H10 5 pent ane C5H12 6 hex ane C6H14 7 hept ane C7H16 8 oct ane C8H18 9 non ane C9H20 10 dec ane C10H22 1 meth ane C H 4 2 eth ane C2H6 s p sp3 atomic orbitals

Alkanes London Dispersion Forces n = 1-4 gases n = 5-15 liquids compound m.w. b.p.(Co) CH4 16 -164 C2H6 30 -88.6 C3H8 44 -42.1 C4H10 58 -0.5 C5H12 72 +36.0 n = 1-4 gases n = 5-15 liquids n > 15 solids

Alkanes IMF = q1q2 r 72 36.1 72 27.9 72 9.5 structural isomers ____ compound m.w. b.p. 72 36.1 72 27.9 72 9.5 structural isomers same formula different shape r  branching

Reactions of Alkanes Substitution of halogens Cl2  2Cl. step 1 initiation step 2 Cl.+ CH4  CH3. + HCl propagation step 3 CH3.+ Cl2  CH3Cl + Cl. propagation step 4 Cl.+ Cl.  Cl2 termination get a mixture of chlorinated methanes

Halogenation of Alkanes CH3Cl chloro methane methyl chloride   CH2Cl2 di chloromethane methylene chloride  CHCl3 tri chloromethane chloroform  CCl4 tetra chloromethane carbon tetrachloride all liquids at room temperature methane is gas e- rich Cl increases LDF dipole moments Which are soluble in H2O? polar solvent

Nomenclature 1. Pick longest C chain as parent 2. Number C beginning at end with first branch 3. Identify branching substituents Assign each a number 4. Use commas to separate numbers hyphens to separate numbers from names 5. Alphabetize substituents

Nomenclature Structural isomers of C5H12 I. III. II. I. pentane II. 2- 4 1 3 2 1 2 2 3 3 4 4 II. 1 1 2 3 I. pentane II. 2- methyl butane III. 2,2- di methyl propane

Nomenclature R = “alkyl” group 1o 3o primary carbon tertiary carbon 4o secondary carbon quaternary carbon

Nomenclature “common” names to learn: iso propyl alphabetized as i sec- butyl alphabetized as b iso butyl alphabetized as i tert- butyl alphabetized as b

Nomenclature heptane heptane heptane 3 branches 2 branches 4 branches 1 2 1 3 7 3 1 3 5 7 4 6 4 2 4 6 5 2 5 6 7 heptane heptane heptane 3 branches 2 branches 4 branches

Nomenclature 3,5-diethyl -2-methyl -4-propyl heptane 2- methyl methyl 1 2 2- methyl methyl 3- ethyl 3 5 7 4 6 4- ethyl propyl propyl 5- ethyl 3,5-diethyl 3,5-diethyl -2-methyl -4-propyl heptane

Cycloalkanes linear alkanes CnH2n+2 branched alkanes cycloalkanes closed rings CnH2n 2 cyclo propane 3 1 bond angle = 60o tetrahedral angle = 109o very unstable

Cycloalkanes cyclobutane bond angle = 88o tetrahedral angle = 109o unstable

Cycloalkanes cyclopentane bond angle = 108o tetrahedral angle = 109o stable

Cycloalkanes cyclohexane predicted bond angle = 120o tetrahedral angle = 109o stable

Cycloalkanes geometric isomers cis- 1,3- dichloro cyclo butane trans- - - cis- 1,3- dichloro cyclo butane trans- 1,3- dichloro cyclo butane

Optical isomerism 3-methyl hexane bromo chloro iodo methane bromo Stereocenter 4 different substituents * * 3-methyl hexane bromo chloro iodo methane * * bromo cyclo pentane trans- 1,3-dibromo cyclopentane no C*

Alkane Summary 1. Alkanes - sp3 hybridized 2. Relatively unreactive Substitution with halogens Combustion 3. Non-polar IMF = London Dispersion Forces size structure

4. Free rotation around C-C bonds conformations 5. Non-cyclic alkanes - structural isomers 6. Cyclic alkanes - geometric isomers cis-, trans- 7. Alkanes - optical isomers stereocenters C*