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summary of functional groups * * EMAIL query?comment

• The primary suffix name (..ene for C=C bond) is based on the longest carbon chain: 2 carbons, ethene; 3 carbons, propene; 4 carbons, butene. After these 4 preserved 'old trivial' names, the name is 'numerically' systematic e.g. 5 carbons, pentene; 6 hexene, 7 heptene etc.
  • e.g. propene, and pent-1-ene
• If the molecule has a ring of carbon atoms including the double bond, the name is prefixed by cyclo…
  • e.g. cyclohexene and ,
  cyclopenta-1,3-diene
• Beyond propene, numbers (e.g. x and y) are needed to indicate the position of the double bond (e.g. …..-x-ene, like pent-1-ene above) or more than one double bond (e.g. …..-x,y-diene, like penta-1,3-diene above and buta-1,3-diene below). These numbers take precedence over substituent numbers and they indicate, via lowest possible number, the first carbon of each C=C double bond which is a higher ranking group than the substituent groups.
  • e.g. hex-3-ene
  • or buta-1,3-diene
• The positions of the substituent(s), denoted with a prefix, e.g. halo… for chloro etc. or alky groups like methyl, ethyl etc., are denoted by using the lowest possible numbers for the associated carbon atoms in the main chain BUT these 'lowest' substituent numbers are determined by the number assigned to the ....ene group, so they can end up seeming a bit high because of the higher ranking ...ene functional group.
  • e.g.
  • 5-methylhex-1-ene, the alkene functional group (C1) is higher ranking than the substituent methyl group (on C5),
  • or   3-chlorobut-1-ene, which is NOT 2-chloro-but-1-ene or 2-chloro-but-2-ene or 2-chloro-but-3-ene etc.
• If there is more than one 'type' of substituent e.g. using the prefixes: bromo…, chloro…, methyl… etc., they are written out in alphabetical order irrespective of carbon atom number (note: di, tri are ignored in using this rule).
• There is a brief note on the formation and structure of poly(alkenes) and the name of the poly(alkene) is readily derived e.g. poly(ethene) [old/everyday names 'polyethylene'/'polythene'] or poly(propene) [old/everyday names 'polypropylene'/'polypropene'] 
• Some 'old' names are quoted in () though their use should be avoided if possible [but many still used - just put one into GOGGLE!].

• The open chain alkenes with one 'ene' group have the general formula C_nH_2n (see examples 1, 2, 6), they are isomeric with cycloalkanes from C₃ onwards
• The open chain alkenes with two 'ene' groups, i.e. dienes, have the general formula C_nH_2n-2 (see examples 4 and 17)
• The cycloalkenes with one 'ene' group in the ring also have the general formula C_nH_2n-2 (see examples 5 and 19)
• The cycloalkenes with two 'ene' groups i.e. cyclodienes, in the ring have the general formula C_nH_2n-4 (see example 20)
• There are many structural isomers in all the above groups, either of the form of chain, positional or functional group isomerism.
• Some 'old' names are quoted in () though their use should be avoided if possible [but many still used - just put one into GOGGLE!].

1. The simplest alkene is ethene (ethylene), molecular formula of , structural formulae are
   •  or and the skeletal formula is only !
   • a substituted ethene: chloroethene (old name 'vinyl chloride'), C₂H₃Cl,  CH₂=CHCl
2. The next open chain alkene is propene (propylene),
   • , , , , ,
   • 1-chloropropene or 1-chloroprop-1-ene:  CH₃-CH=CHCl

     2-chloropropene or 2-chloroprop-1-ene:  CH₃-CCl=CH₂

     3-chloropropene or 3-chloroprop-1-ene:  ClCH₂-CH=CH₂

3. Methylpropene or 2-methylpropene, but 2- is not really needed here, (isobutene, isobutylene), is the simplest branched open chain alkene, , ,
4. Propadiene, (propa-1,2-diene, but the numbers NOT needed), is the simplest possible open chain 'diene', that is, with two C=C double bonds in the molecule,
   • , , ,
5. The simplest cycloalkene is cyclopropene, , , ,
6. But-1-ene (1-butene) is the first alkene, without substituent groups, where a positional number is needed,
   • ,
   • 1-chlorobut-1-ene:  CH₃-CH₂-CH=CHCl

     2-chlorobut-1-ene:  CH₃-CH₂-CCl=CH₂ 

     3-chlorobut-1-ene:  CH₃-CHCl-CH=CH₂ 

     4-chlorobut-1-ene:  ClCH₂-CH₂-CH=CH₂

7. 2-methylbut-1-ene, ,
8. 3-methylbut-1-ene, , ,
9. 2,3-dimethylbut-1-ene, ,
10. 3,3-dimethylbut-1-ene, ,

11. 2,3,3-trimethylbut-1-ene, ,
12. But-2-ene (2-butene) is the first alkene (with no substituent groups) to have geometrical isomers of
    •  , , but the latter doesn't show the two different spatial arrangements possible due to a high energy barrier to rotation about the double bond,
    • or is cis-but-2-ene,
    •  or is trans-but-2-ene,
    • in simple cases, with two identical/similar groups, the trans isomer has these groups 'diagonally' opposite and the cis isomer has the groups at a 'right angle' to each other)

13. 1-chlorobut-2-ene:  CH₃-CH=CH-CH₂Cl

14. 2-chlorobut-2-ene:  CH₃-CH=CCl-CH₃

15. 2-methylbut-2-ene, does not have geometrical isomers because there are two identical groups (CH₃) attached to the same carbon of the double bond

,

• ,

, does not have geometrical isomers because there are two identical groups (CH₃) attached to the same carbon of the double bond,

16. 2,3-dimethylbut-2-ene, ,

, does not have geometrical isomers because there are two identical groups attached to the same carbon of the double bond,

17. buta-1,2-diene (note the a after the but), is the next simplest diene after propadiene, i.e. with two C=C double bonds,

    •  , , ,

18. buta-1,3-diene (note the optional a after the but), is the next diene i.e. 2 C=C double bonds and isomeric with buta-1,2-diene (above),

    • , , and has two geometrical isomers,

    • cis-buta-1,3-diene

    •  , and

    • trans-buta-1,3-diene ,

    • (2-methylbuta-1,3-diene is the synthetic rubber 'isoprene') 

19. Cyclobutene is the next simplest cyclo-alkene after cyclopropene

    • , , ,

20. Cyclobuta-1,3-diene is the simplest cyclo-diene that exists, , ,



21. Pent-1-ene, , ,

22. 2-methylpent-1-ene, ,

23. 3-methylpent-1-ene, ,

24. 4-methylpent-1-ene, ,

25. 2,3-dimethylpent-1-ene, ,

26. 2,4-dimethylpent-1-ene, ,

27. 3,3-dimethylpent-1-ene, ,

28. 3,4-dimethylpent-1-ene, ,

29. 4,4-dimethylpent-1-ene, ,

30. 3-ethylpent-1-ene, ,



31. Pent-2-ene, , , has geometrical isomers:

    • cis- and trans-

32. 2-methylpent-2-ene, ,

, has no geometrical isomers.

33. 3-methylpent-2-ene, , has two geometrical isomers:

    •  , ,

    • and   ,

34. 4-methylpent-2-ene, , has two geometrical isomers:

    • cis- , , trans-

35. 2,3-dimethylpent-2-ene,

36. 2,4-dimethylpent-2-ene,

37. 3,4-dimethylpent-2-ene, ,

    • it has two geometrical isomers: cis- , and trans

38. 4,4-dimethylpent-2-ene, , has two geometrical isomers:

    • cis- , and trans-

39. 3-ethylpent-2-ene, , ,

    • no geometrical isomers because there are two identical groups attached to the same carbon of the double bond

40. Cyclopentene, , ,



41. Cyclopenta-1,3-diene, ,

42. Hex-1-ene, , ,

43. 2-methylhex-1-ene, , 

• 42. - 46. have no geometrical isomers because there are two identical groups (H) attached to the same carbon of the double bond

.

44. 3-methylhex-1-ene, ,

45. 4-methylhex-1-ene, ,

46. 5-methylhex-1-ene, ,

47. Hex-2-ene, , two geometrical isomers:

    • cis- , , and

    •  trans-, ,

48. 2-methylhex-2-ene, ,

49. 3-methylhex-2-ene, ,

    • has two geometrical isomers: and

50. 4-methylhex-2-ene, ,

    • has two geometrical isomers: cis- , and trans-

    

51. 5-methylhex-2-ene, , has two geometrical isomers:

     cis- and trans-

52. Hex-3-ene, , has two geometrical isomers:

    • cis- , trans-

53. 2-methylhex-3-ene, , has geometrical isomers:

    •  cis- and trans-

54. 3-methylhex-3-ene, has geometrical isomers:

    • cis- and trans-

55. Cyclohexene, , ,

56. Cyclohexa-1,3-diene, ,

57. Cyclohexa-1,4-diene, , ,

58. hept-1-ene, , , , no geometrical isomers

59. hept-2-ene, , ,

    • has geometrical isomers: cis- and trans-

60. hept-3-ene, ,

    • has geometrical isomers: cis- and trans-

1.   chloroethene

2.   1-chloropropene

3.   2-chloropropene

4.   3-chloropropene

5.   1-chlorobut-1-ene

6.   2-chlorobut-1-ene

7.   3-chlorobut-1-ene

8.   4-chlorobut-1-ene

9. 1-chlorobut-2-ene

10.   2-chlorobut-2-ene