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Organic Chemistry

Organic Chemistry. CH30S. Structural formula. Condensed structural formula. n 1 2 3 4 5 6. Molecular Formula CH 4 C 2 H 6 C 3 H 8 C 4 H 10 C 5 H 12 C 6 H 14. Name. methane. ethane. propane. butane. pentane. hexane.

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Organic Chemistry

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  1. Organic Chemistry CH30S

  2. Structural formula Condensed structural formula n 1 2 3 4 5 6 Molecular Formula CH4 C2H6 C3H8 C4H10 C5H12 C6H14 Name methane ethane propane butane pentane hexane

  3. 1. The alkane series is generated by repeatedly adding ‘CH2’ to the previous member of the series A series generated in this manner is known as a homologous series 2. Nomenclature (naming) Names all share a common suffix, i.e.’ …ane’ The suffix ‘…ane’ indicates that the compound is an alkane The prefix indicates the number of carbons in the compound

  4. ‘Hept…’ = 7 Carbons ‘Meth…’ = 1 Carbon ‘Oct…’ = 8 Carbons ‘Eth…’ = 2 Carbons ‘Non…’ = 9 Carbons ‘Prop…’ = 3 Carbons ‘But…’ = 4 Carbons ‘Dec…’ = 10 Carbons ‘Undec…’ = 11 Carbons ‘Pent…’ = 5 Carbons ‘Hex…’ = 6 Carbons ‘Dodec…’ = 12 Carbons Heptane CH3CH2CH2CH2CH2CH2CH3 ‘Hept…’ implies 7 Carbons ‘…ane’ implies compound is an alkane

  5. 3. Representation and conformation • Structural formulae: give information on atom-to-atom connectivity • Do not give information on stereochemistry (3D orientation) Same structural formula Have the same information content

  6. Simple alkanes have conformational freedom at room temperature i.e. have rotation about C-C bonds the most stable (lowest energy) conformation for these is the all staggered ‘straight chain’; there is minimal ‘steric hindrance’ between adjacent hydrogen electron clouds e.g. for hexane

  7. 4. Representing larger molecules Full structural formula for, e.g. octane Condensed structural formula Line segment structural formula

  8. Line segment structural formula for octane • Each line represents a covalent bond between atoms • C-H bonds not shown, assume they are present • [so as make up valence total for Carbon to 4]

  9. Generating the series of alkanes by incrementally adding ‘CH2’ However, the last increment could also give

  10. Structural isomers ‘Isomer’, from Greek isos (equal) and meros (in part) • Structural isomers: same molecular formulae • Different structural formulae • (different atom-to-atom connectivity)

  11. Structural isomers: different physical properties • Are different chemical entities

  12. Pentane C5H12 3 structural isomers • All of these based on tetrahedral (sp3 hybridised) Carbon • No other arrangements of C5H12 possible

  13. Need to expand the system of nomenclature to allow naming of individual structural isomers • Compounds without branches are called ‘straight chains’ • Branched compounds are named as alkyl derivatives of the longest straight chain in the molecule • The length of the longest chain provides the parent name • The straight chain is numbered to allow indication of the point of branching • The branching alkyl groups (or substituents) are named from the corresponding alkane

  14. AlkaneAlkyl group Methane Methyl (CH3-) Ethane Ethyl (CH3CH2-) Propane Propyl (CH3CH2CH2-) Butane Butyl (CH3CH2CH2CH2-) Etc. 2-Methylbutane [Straight chain numbered so as to give the lower branch number]

  15. 1. First, identify longest straight chain ‘…nonane’ 2. Number so as to give lower numbers for branch points Branches at C3 and C6 Not at C4 and C7 3,6-Dimethyl-6-ethylnonane

  16. 3. Identical substituents grouped together with a prefix • ‘di…’ for two identical • ‘tri…’ for three • ‘tetra…’ for four 4. Substituents named in alphabetical order

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