Alkanes and Alkane Isomers Isomers TABLE 3.2 Number of Alkane Isomers From the Greek isos meros Number of meaning“made of the same parts” Formula isomers Compounds that have the same C6H14 5 molecular formula but different C7H16 9 C8H18 18 structures CgH20 35 C10H22 75 C15H32 4,347 C20H42 366,319 C30H62 4,111,846,763 CH3 CH3CH2CH2CH2CH3 CHaCH2CHCH3 CH3 Pentane,CsH12 2-Methylbutane.CsH12 2.2-Dimethylpropane.CsH12
Isomers ▪ From the Greek isos + meros meaning “made of the same parts” ▪ Compounds that have the same molecular formula but different structures Alkanes and Alkane Isomers
Alkanes and Alkane Isomers Constitutional isomers Isomers that have the same kinds and numbers of atoms that are connected in different arrangements May have different carbon skeletons,different functional groups,or different position of the functional groups Different carbon CH3 skeletons C4H10 CH3CHCH3 and CH3CH2CH2CH3 2-Methylpropane Butane (isobutane) Different functional CH3CH20H and CH3OCH3 groups C2H60 Ethanol Dimethyl ether Different position of NH2 functional groups C3HgN CH3CHCH3 and CH3CH2CH2NH2 Isopropylamine Propylamine
Constitutional isomers ▪ Isomers that have the same kinds and numbers of atoms that are connected in different arrangements ▪ May have different carbon skeletons, different functional groups, or different position of the functional groups Alkanes and Alkane Isomers
Alkanes and Alkane Isomers -A given alkane can be drawn arbitrarily in many ways Representations of butane n-C4H10 where n denotes normal (straight-chain) HHHH H-C-C一C-C-H HHHH These representations indicate only the connections among atoms These representations do not imply any particular three- dimensional geometry Chemists rarely draw all the bonds in a molecule and usually refer to the condensed structure CH3-CH2-CH2-CH3 CH3CH2CH2CH3 CH3(CH2)2CH3
▪ A given alkane can be drawn arbitrarily in many ways ▪ Representations of butane n-C4H10 where n denotes normal (straight-chain) ▪ These representations indicate only the connections among atoms ▪ These representations do not imply any particular threedimensional geometry ▪ Chemists rarely draw all the bonds in a molecule and usually refer to the condensed structure Alkanes and Alkane Isomers
Alkanes and Alkane Isomers Names of straight-chain alkanes Named according to the number of carbon atoms in the molecule,with the exception of the first four -Names based on Greek numbers Suffix-ane added to identify the molecule as alkane TABLE33 Names of Straight-Chain Alkanes Number of Formula Number of Formula carbons(n) Name (CnH2n+2) carbons (n) Name (CnH2n+2) 1 Methane CH4 8 Octane C8H18 2 Ethane C2H6 9 Nonane CgH20 3 Propane C3H8 10 Decane C10H22 4 Butane C4H10 11 Undecane C1H24 5 Pentane CsH12 12 Dodecane C12H26 6 Hexane C6H14 20 Icosane C20H42 7 Heptane C7H16 30 Triacontane C30H62
▪ Names of straight-chain alkanes ▪ Named according to the number of carbon atoms in the molecule, with the exception of the first four ▪ Names based on Greek numbers ▪ Suffix –ane added to identify the molecule as alkane Alkanes and Alkane Isomers
Worked Example 3.1 Drawing the Structures of Isomers Propose structures for two isomers with the formula C2H-N
Propose structures for two isomers with the formula C2H7N. Worked Example 3.1 Drawing the Structures of Isomers