1 2.5 Introduction to Alkanes Methane, Ethane, Propane Figure 2.7 - PDF document

Carey Chapter 2 – Hydrocarbon Frameworks “Alkanes” 2.2-2.3 Chemical Bonding Figure 2.3 – Valence bond picture for H 2 2.4 Molecular orbitals by combining two atomic orbitals Figure 2.6 1

2.5 Introduction to Alkanes – Methane, Ethane, Propane Figure 2.7 CH 4 CH 3 CH 3 CH 3 CH 2 CH 3 b.p. -160 o C -89 o C -42 o C 2.6 sp 3 Hybridization and bonding in Methane Figure 2.9 2.6 sp 3 Hybridization and bonding in Methane Figure 2.10 2

2.7 sp 3 Hybridization and bonding in Ethane Figure 2.11 2.8 Isomeric alkanes – the Butanes Structural Isomers C 4 H 10 n -butane C 4 H 10 isobutane 2.9-2.10 Higher alkanes – the C 5 H 12 isomers C 5 H 12 C 5 H 12 C 5 H 12 n -pentane isopentane neopentane 2.10 Higher alkanes – diversity 3

Careful with drawing chains! CH 3 CHCH 2 CH 3 CH 3 CH 2 CHCH 3 CH 3 CH 3 CH 3 CHCH 2 CH 3 CH 3 CH 3 CH 3 CH 2 CH 2 CH 3 CH 3 CH 2 CHCH 3 CH 3 All the same compound 2.11-2.12 Alkane nomenclature Need to know up to C-12 2.11-2.12 Alkane nomenclature IUPAC Rules: • Find the longest continuous carbon chain • Identify substituent groups attached to the chain • Number the chain so as to keep numbers small • Write the name in the following format: Numerical location - [substituent(s)][parent alkane] e.g. 2,3-dimethylheptane 4

2.12 IUPAC Rules and how to apply them Hexane (IUPAC); n -hexane (common) Longest chain - hexane substituent - meth yl position on chain - 2 2-methylhexane not 5-methylhexane 3,4-dimethylheptane 2.13 Alkyl groups Replace -ane ending with -yl H C C C C C C C C H H C primary (1 o ) secondary (2 o ) tertiary (3 o ) H H H CH 3 CH 3 H C C C CH H 3 C C CH 3 H H H CH 3 (CH 3 ) 3 C CH 3 CH 2 CH 2 (CH 3 ) 2 CH propyl group isopropyl group t -Butyl group 1-methylethyl 1,1-dimethylethyl 2.14 Highly branched alkanes 4-ethyloctane 4-ethyl-3-methyloctane 4-ethyl-3,5-dimethyloctane 5

2.15 Cycloalkanes 1,1,3-trimethylcyclohexane 2-ethyl-1,1- dimethylcyclopentane C(CH 3 ) 3 (notice the “di” is not (1,1-dimethylethyl)cycloheptane involved in the alphabetization) 2.16 Sources of alkanes and cycloalkanes Figure 2.12 2.17 Physical properties 6

2.17 Physical properties – branched alkanes 2.18 Chemical properties of Alkanes Alkane properties: • Generally very insoluble in water (“greasy” or “oily”) • Individual molecules interact via van der Waals forces • These intermolecular forces decrease with branching • Alkanes may be combusted in oxygen: e.g. CH 4 + 2O 2 CO 2 + 2H 2 O ∆ H = - 213 kcal i.e combustion of hydrocarbons releases energy 2.18 Heats of combustion – Figure 2.15 7

2.19 Oxidation-Reduction in Organic Chemistry 2.20 sp 2 Hybridization in ethylene H H C C H H 2.20 sp 2 Hybridization in ethylene Figure 2.17 8

2.20 sp 2 Hybridization in ethylene Figure 2.18 2.21 sp Hybridization in acetylene Figure 2.20 2.21 sp Hybridization in acetylene Figure 2.21 9