1 2.2-2.3 Chemical Bonding Two Possibilities Figure 2.5 bond and - PDF document

Carey Chapter 2 – Hydrocarbon Frameworks : “Alkanes” YSU YSU 2.2-2.3 Chemical Bonding Figure 2.3 – Valence bond picture for H 2 YSU YSU 1

2.2-2.3 Chemical Bonding – Two Possibilities Figure 2.5 – bond and antibond possibilities for H 2 YSU YSU 2.4 Molecular orbitals by combining two atomic orbitals Figure 2.6 – bond and antibond possibilities for H 2 YSU YSU 2

2.5 Introduction to Alkanes – Methane, Ethane, Propane CH 4 CH 3 CH 3 CH 3 CH 2 CH 3 b.p. -160 o C -89 o C -42 o C Figure 2.7 – Low molecular weight alkanes YSU YSU 2.6 sp 3 Hybridization and bonding in Methane Figure 2.9 – Hybridization picture for C in CH 4 YSU YSU 3

2.6 sp 3 Hybridization and bonding in Methane Figure 2.10 – Hybrid orbital picture for C in CH 4 YSU YSU 2.7 sp 3 Hybridization and bonding in Ethane Figure 2.11 – sp 3 -sp 3 interaction in ethane YSU YSU 4

2.8 Isomeric alkanes – the Butanes Structural Isomers C 4 H 10 n ‐ butane C 4 H 10 isobutane YSU YSU 2.9-2.10 Higher alkanes – the C 5 H 12 isomers Structural Isomers C 5 H 12 C 5 H 12 C 5 H 12 neopentane isopentane n ‐ pentane YSU YSU 5

2.10 Higher alkanes – diversity YSU YSU Careful with drawing chains! CH 3 CHCH 2 CH 3 CH 3 CH 3 CH 2 CHCH 3 CH 3 CH 3 CH 3 CHCH 2 CH 3 CH 3 CH 3 CH 2 CH 2 CH 3 CH 3 CH 2 CHCH 3 CH 3 All the same compound! YSU YSU 6

2.11-2.12 Alkane nomenclature - Need to know up to C-12 YSU YSU 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 YSU YSU 7

2.12 IUPAC Rules and how to apply them Hexane (IUPAC); n ‐ hexane (common) 2 ‐ methylhexane not 5 ‐ methylhexane 2,4 ‐ dimethylheptane YSU YSU 2.13 Alkyl groups - Classes 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 ) YSU YSU 8

2.13 Alkyl groups - Common H H H CH 3 CH 3 C H C C C H 3 C C H CH 3 H H H CH 3 CH 3 CH 2 CH 2 (CH 3 ) 2 CH (CH 3 ) 3 C propyl group isopropyl group t ‐ butyl group (1 ‐ methylethyl) (1,1 ‐ dimethylethyl ) YSU YSU 2.14 Highly branched alkanes 4 ‐ ethyloctane 4 ‐ ethyl ‐ 3 ‐ methyloctane 4 ‐ ethyl ‐ 3,5 ‐ dimethyloctane YSU YSU 9

2.15 Cycloalkanes 1,1,3 ‐ trimethylcyclohexane 2 ‐ ethyl ‐ 1,1 ‐ dimethylcyclopentane C(CH 3 ) 3 (notice the “di” is not involved in (1,1 ‐ dimethylethyl)cycloheptane the alphabetization) YSU YSU 2.16 Sources of alkanes and cycloalkanes Figure 2.12 – Various fractions obtained from crude oil YSU YSU 10

2.17 Physical properties Figure 2.15 – Boiling point versus number of carbons YSU YSU 2.17 Physical properties – branched alkanes Figure 2.16 – How branching has an effect on properties YSU YSU 11

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: CO 2 + 2H 2 O  H = ‐ 213 kcal e.g. CH 4 + 2O 2 i.e combustion of hydrocarbons releases energy YSU YSU 2.18 Heats of combustion – Figure 2.17 YSU YSU 12

2.19 Oxidation-Reduction in Organic Chemistry YSU YSU 2.20 sp 2 Hybridization in ethylene H H C C H H Figure 2.18 – Different representations of ethene YSU YSU 13

2.20 sp 2 Hybridization in ethylene Figure 2.19 – Hybrid orbitals required for ethylene YSU YSU 2.20 sp 2 Hybridization in ethylene Figure 2.20 YSU YSU 14

2.21 sp Hybridization in acetylene Figure 2.22 YSU YSU 2.21 sp Hybridization in acetylene Figure 2.21 Figure 2.23 YSU YSU 15