1	Chemistry 121(01) Winter 2009
2	Chapter 12. Saturated Hydrocarbons Sections 12.4-12.14 & 12.6
3	Chapter 12. Saturated Hydrocarbons
4	Types of formula for organic compounds
5	Alicyclic Alkanes
6	Organic Nomenclature Organic molecules can be very complex. Naming system must be able to tell Number of carbons in the longest chain The location of any branches Which functional groups are present and where they are located. The IUPAC Nomenclature System provides a uniform set of rules that we can follow.
7	Naming alkanes 1 Find the longest carbon chain. Use as base name with an ane ending. 2 Locate any branches on chain. Use base names with a yl ending. 3 For multiple branch of the same type, modify name with di, tri, ... 4 Show the location of each branch with numbers. 5 List multiple branches alphabetically - the di, tri, ... don’t count..
8	Alkanes First four members of the alkanes Name # of C Condensed formula Methane 1 CH₄ Ethane 2 CH₃CH₃ Propane 3 CH₃CH₂CH₃ Butane 4 CH₃CH₂CH₂CH₃ Called a homologous series “Members differ by number of CH₂ groups”
9	Nomenclature: Unbranched or straight chain alkanes General molecular formula: C_nH_2n+2 All bond angles about tetrahedral carbon are approximately 109.5°
10	Isomerism Isomers - different compounds having the same molecular formula but different structural formulas There are two type of Isomers: Constitutional isomerism: Different connections among atoms in the Skeleton Position Functional group Stereoisomerism: Same connectivity among atoms, but these atoms differ in spatial orientation geometric conformational optical
11
12	Constitutional isomers in butane Constitutional isomers: compounds with the same molecular formula but a different connectivity of their atoms in the skeleton. There are two constitutional isomers with molecular formula C₄H₁₀
13
14	Rules of IUPAC Nomenclature of Branched Alkanes Parent name: the longest carbon chain Substituent: a group bonded to the parent chain Alkyl group: a substituent derived by removal of a hydrogen from an alkane; given the symbol R- written in alphabetical order CH₄ becomes CH₃- (methyl) CH₃CH₃ becomes CH₃CH₂- (ethyl) Prefixes: di-, tri-, tetra-, etc. are not included in alphabetization
15	Common alkyl groups
16	Names of Alkyl Groups methyl H₄ methane: CH₃- methyl ethyl CH₃CH₃ethane: CH₃CH₂- ethyl propyl CH₃CH₂CH₂- isopropyl (CH₃)₂CH- butyl CH₃CH₂CH₂CH₂- sec-butyl CH₃CH₂(CH₃)CH- isobutyl (CH₃)₂CHCH₂- tert-butyl (CH₃)₃C-
17	IUPAC Nomenclature of branched alkanes suffix -ane specifies an alkane prefix tells the number of carbon atoms
18	Example
19
20
21	Giving IUPAC names CH₃C(CH₃)₂CH₂CH(CH₂CH₃)CH₂CH₃
22	Types of carbon and hydrogen atoms Primary (1°) carbon: a C bonded to one other carbon Secondary (2°) carbon : a C bonded to two other carbons Tertiary (3°) carbon : a C bonded to three other carbons Quaternary (4°) carbon : a C bonded to four other carbons Primary (1°) hydrogen: a H bonded to primary (1°) carbon Secondary (2°) hydrogen : a H bonded to secondary (2°) carbon Tertiary (3°) hydrogen : a H bonded to tertiary (3°) carbon
23
24	Staggered and Eclipsed conformations of alkanes and cycloalkanes Conformation Stereoisomerism: Any three-dimensional arrangement of atoms in a molecule that results from rotation about a single bond Staggered conformation: A conformation about a carbon-carbon single bond where the atoms on one carbon are as far apart as possible from the atoms on an adjacent carbon
25	Conformations of Alkanes Conformers shown by Newman Projections Ethane :staggered, ecliped Butane: two staggered and two ecliped conformations
26	"Eclipsed conformation" Eclipsed conformation: a conformation about a carbon-carbon single bond in which the atoms on one carbon are as close as possible to the atoms on an adjacent carbon Lowest energy conformation of an alkane is a fully staggered conformation. The torsional strain between staggered and eclipsed ethane is approximately 3.0 kcal (12.6 kJ)/ mol
27	Sources of Alkanes Natural gas 90-95% methane, 5-10% ethane Petroleum gases (bp below 20°C) naphthas, including gasoline (bp 20 - 200°C) kerosene (bp 175 - 275°C) fuel oil (bp 250 - 400°C) lubricating oils (bp above 350°C) asphalt (residue after distillation) Coal
28	Molecular Structure and Physical Properties
29	Alkanes Physical Properties Nonpolar molecules Not soluble in water Low density Low melting point Low boiling point
30	Physical Properties of Alkanes Name bp, ^oC mp, ^oC Density at 20 ^oC Methane -161.7 -182.6 0.000667 Ethane - 88.6 -182.8 0.00125 Propane - 42.2 -187.1 0.00183 Butane -0.5 -135.0 0.00242 Pentane 36.1 -129.7 0.626 Hexane 68.7 - 94.0 0.659 Heptane 98.4 - 90.5 0.684 Octane 125.6 - 56.8 0.703 Nonane 150.7 -53.7 0.718 Decane 174.0 -29.7 0.730
31
32	Constitutional isomerism in alkane The number of constitutional isomerism increases with the carbon number in the alkane
33	Physical Properties Constitutional isomers Constitutional isomers are different compounds and have different physical properties
34	Reactions of alkanes Halogenation A reaction where a halogen replaces one or more hydrogens. CH₄(g) + Cl₂(g) CH₃Cl(g) + HCl(g) Used to prepare many solvents dichloromethane - paint stripper chloroform - once used as anesthesia 1,2-dichloroethane - dry cleaning fluid
35	Reactions of alkanes Combustion CH₄(g) + 2O₂(g) CO₂(g) + 2H₂O(g) Many alkanes are used this way - as fuels Methane - natural gas Propane - used in gas grills Butane - lighters Gasoline - mixture of many hydrocarbons,
36	Reactions of Alkanes Oxidation is the basis for the use of alkanes as energy sources for heat and power heat of combustion: heat released when one mole of a substance is oxidized to carbon dioxide and water in a combustion reaction.
37	Synthesis Gas A mixture of carbon monoxide and hydrogen in varying proportions, depending on how it is produced Methanol and acetic acid are produced from synthesis gas
38	Cycloalknes Cyclic alkanes: General molecular formula, C_nH_2n Structure and nomenclature named similar to noncyclic alkanes to name, prefix the name of the corresponding open-chain alkane with cyclo-, and name each substituent on the ring if only one substituent, no need to give it a number if two substituents, number from the substituent of lower alphabetical order if three or more substituents, number to give them the lowest set of numbers, and then list substituents in alphabetical order in planar cyclopentane, all C-C-C bond angles are 108°, which differ only slightly from the tetrahedral angle of 109.5°consequently there is little angle strain
39
40
41
42	Cycloalkanes :saturated hydrocarbons with a carbon ring Have C-C single bonds in a ring structure. General formula C_nH_2n
43	Naming Cycloalkanes Have the carbons connected in a ring. These compounds are known collectively as To name a cycloalkane, use the prefix cyclo- with the parent. If there is only one substituent, a number is not needed.
44	Conformations of Cycloalkanes Cyclohexane Chair conformation-low energy Boat conformation-higher energy
45	Geometrical (cis & trans) Isomers of Cycloalkanes Carbon ring create a rigid structure trans and cis is used to describe the arrangements of alkyl groups with respect to the plane of the ring cis: on the same side trans: on the opposite sides
46	Cis and trans Geometrical isomers of Cycloalkanes two groups are said to be located cis to each other if they lie on the same side of a plane. If they are on opposite sides, their relative position is described as trans.
47
48
49
50
51	Interconversions of conformations Interconvert ion to alternative chair conformations (lower energy) via a boat conformation (higher energy
52	Cis and Trans Geometric Isomerism in Cycloalkanes
53
54	"Problem" Problem: draw the alternative chair conformations of this trisubstituted cyclohexane and state which is the more stable