1. IUPAC
NOMENCLATURE
BY:- Mr. Mangesh S. Ghodke

2. Drawing Organic Structures
The International Union of Pure and Applied Chemistry (IUPAC)
Drawing Organic Structures
A two-dimensional structural formula of a hydrocarbon shows all of the atoms with all of their bonds in the plane of the page
Hydrocarbons are compounds composed only of carbon and hydrogen atoms.

3. A condensed structural formula includes all of the atoms but uses line bonds to emphasize the main structural characteristics of the molecule.

4. Bond-line formulas represent the carbon atoms as the intersection of lines and as line ends.

5. Unbranched Chains The Alkanes (CnH2n+2)
The first four (n=1-4) unbranched chain saturated hydrocarbons are called methane, ethane, propane and butane. After this, there is a numerical term (of Greek origin) followed by the ending "-ane". The first twelve members are given in Table 1.
The group derived from one of these alkanes by removal of a terminal (end) hydrogen is called an alkyl group. The group name is found by removing "ane" from the alkane name and adding “y".
Example: CH3-CH2-CH2-CH3 butane
becomes CH3-CH2-CH2-CH2- butyl

7. B. Branched Chains
The following steps are taken in naming an alkane with a branched chain:
(a) Find the longest continuous carbon chain and select the appropriate alkane name from Table 1. (Side chains are not included in the carbon count.)
(b) Name all of the side chains (carbon chains attached to the longest chain) and list them in alphabetical order. Ignore multiplicative prefixes such as “di-“ (2), “tri-“ (3), "tetra-" (4) etc. Also ignore "sec-" and "tert-" but not "iso".
(c) Number the longest chain so that substituents have the lowest possible numbers and insert location numbers before each of the side chain names.

10. Branched side chains are named by renumbering the alkyl group giving the carbon with the free valence (i.e. point of attachment to the main chain) the number 1 and giving substituents the appropriate number in the usual way.

12. In the following structure numbering from the right end gives lower numbers than when numbered from the left end. Thus, the structure’s name is 2,3,5-trimethylhexane and not 2,4,5-trimethylhexane.

13. The same principles apply to naming a compound when its bond-line formula is given. The colored screen on the right indicates the longest chain for the following compound.
The colored screen covers nine carbons. To simplify the way the drawing looks, redraw the longest chain straightened and number the carbon atoms as shown below

14. A Summary of the Steps Used to Name an Alkane:
Step 1 Find the longest possible chain of carbon atoms. Name this chain based on the number of carbons in this chain. If there is more than one chain of the same length, choose the one with the simpler substituents.
Step 2 Number the carbons on the longest chain. Begin numbering from the end closest to a substituent on the chain.
Step 3 Name any substituents using the alkane name for the number of carbons in the chain, changing the –ane suffix to –yl.
Step 4 List the names of the substituents alphabetically. Precede each substituent with a number and a dash. Immediately follow the last substituent by the name of the longest chain.
Step 5 If there are multiple instances of a substituent, list the substituent name with the prefix di–, tri–, etc., indicating the number of identical substituents. Number each substituent and separate the numbers with commas.

15. Naming Alkenes (ii) The Alkenes (CnH2n) One double bond
Step 1 Find the longest continuous chain of carbon atoms containing the double bond. This is the parent chain.
Step 2 Name this chain by replacing the —ane ending of the name of the alkane chain of the same length with —ene.
Step 3 Indicate the position of the double bond by numbering the parent chain from the end that gives the first carbon of the double bond the lowest number. Here are two examples that show how to number
Special Note
CH2 CH2
has the special name “ethylene”.

16. Step 1 Find the longest chain of carbons containing the double bond
Step 1 Find the longest chain of carbons containing the double bond. It contains six carbons.
Step 2 Name the parent chain. Its name is hexene.
Step 3 Determine the position of the double bond in the parent chain. In this case, you number the parent chain from right to left because that gives the first carbon of the double bond the lowest number. The parent name is 2-hexene
Step 4 Number and name the substituents. The compound has two methyl groups bonded to C4.

17. Step 5 Put together all the pieces of the name
Step 5 Put together all the pieces of the name. The compound's complete name is 4,4-dimethyl-2-hexene.

18. B. More than one double bond
(a) Find and name the longest carbon chain containing the maximum number of
double bonds.
(b) Change the "ane" of the alkane name to:
"adiene" 2 double bonds
"atriene" 3 double bonds
"atetraene" 4 double bonds etc.
(c) Number the chain so as to give the double bonds the lowest possible numbers.
(d) Name the alkyl side chains in the usual way.

19. Step 1 Determine the length of the parent chain and the positions of the double bonds. The parent chain is six carbons long. There are two double bonds, and their positions are C1 and C4.
Step 2 Write the numbers of the locations of the double bonds followed by a hyphen: 1,4–.
Step 3 After the hyphen write the name of the parent chain with the –diene ending. The name of the compound is 1,4-hexadiene

20. An alkenyl group is a side chain containing a double bond
Step 1 Start numbering from the carbon that bonds the side chain to the parent chain.
Step 2 When naming the side chain, use the —enyl suffix instead of —ene. Parentheses are often required so that you know the number belongs with the side chain.

21. (iii) The Alkynes (CnH2n-2)
Alkynes are hydrocarbons that contain one or more carbon—carbon triple bonds. These are named in identical fashion to alkenes except that "ene" in the alkene name isreplaced by:
“yne" 1 triple bond
"adiyne" 2 triple bonds
"atriyne" 3 triple bonds etc.

22. Step 1 Find the parent chain
Step 1 Find the parent chain. As with alkenes, it must contain the triple bond. The parent chain contains five carbons.
Step 2 Name the parent chain by substituting the —yne ending for the —ane ending of the parent carbon chain. The name of the parent chain is pentyne.
Step 3 Indicate the position of the triple bond by numbering the parent chain from the end that gives the first carbon of the triple bond the lowest number. The position of the triple bond is C2.
Step 4 Place the number of the position of the triple bond first, followed by a hyphen followed by the name of the parent chain. The name of the compound is 2-pentyne.

23. (iv) Combined Alkenes and Alkynes
If a compound has double and triple bonds then the longest chain is selected so as to contain the maximum number of double and triple bonds and is named by replacing the "ane" of the corresponding alkane by "en(e)", "adien(e)" etc. followed by "yne", "diyne" etc. The "e" is omitted before a vowel or a "y“. The chain is numbered so as to give the lowest numbers to the double bonds, then triple bonds

24. Step 1 Find the longest continuous chain containing both the double and triple bonds.
Step 2 Number the chain so that the multiple bonds get the lowest possible numbers.
Step 3 Number the position of the double bond on the parent chain. In the following example that is C1.
Step 4 Use the —en ending to indicate the name of the parent chain. The parent chain contains six carbons, so that gives the name hexen—.

25. Step 5 For the triple bond, use the —yne ending along with the number identifying the triple bond's position on the parent chain. Number the parent chain so that either the double or triple bond takes precedence over any other substituent, irrespective of whether the —en or —yne gets the lowest number. The name of the example compound is 1-hexen-4-yne.
However, when both groups could get the same number, the –en takes priority and receives the lower number.

26. Groups derived from alkenes, alkynes or combined hydrocarbons are named by dropping the final "e" and replacing it by "yl". The chain is renumbered to give the carbon with the free valence the number 1 position:

27. (v) Cyclic Hydrocarbons
Compounds with hydrocarbon rings are named by the insertion of "cyclo"- before the name of the hydrocarbon corresponding to the open chain compound containing the same number of carbons.

28. Naming Cycloalkanes
Step 1 Determine the parent name of the compound by counting the number of carbons in the ring. Use the same parent name for the ring that you would use for the normal alkane containing that number of carbons
Step 2 Add the prefix cyclo– to the parent name
Step 3 Name any alkyl group substituents the same way that you name any other alkyl group

29. Step 4 Determine the position of the alkyl group or groups on the ring.
a. For a ring with only one alkyl group attached, you do not need a number to designate the group's position. The carbon bearing a single group is always carbon number 1.
b. When a ring has more than one alkyl group attached, number the ring to give the lowest sum of numbers. If there are two groups, assign the number one to the first alkyl group alphabetically. Then count the shortest distance to the second substituent. For example, the following compoundis 1-ethyl-2-methylcyclohexane, not 1-ethyl-6-ethylcyclohexane:

30. c. If the sum of numbers is identical either direction around the ring, then count towards the second group alphabetically on the ring. The following compound is 1-ethyl-3-methyl-5-propylcyclohexane
Step 5 When the alkane chain is complex or has more carbons than the ring, name the ring as a substituent on the alkane chain. Follow the above steps for naming a normal alkane and for naming a cycloalkane. Call the ring a cycloalkyl group

31. Step 6 When one ring is attached to another ring, call the larger ring the parent compound. Use the above steps for naming the cycloalkane and cycloalkyl portions of the compound.
When naming molecules with a cycloalkyl substituent, consider the prefix cyclo– when alphabetizing

32. Naming cycloalkenes is similar to naming alkenes, except that you number the ring so that the double bond is between C1 and C2.
For example, the following compound is 3-methylcyclohexene, not 2-methylcyclohexene.

33. Step 1 Determine and name the parent chain
Step 1 Determine and name the parent chain. The parent chain is a ring with six carbons. It also contains two double bonds. Thus, the name of the parent chain is cyclohexadiene.
Step 2 Determine the positions of the double bonds. Remember that you want to number in such a way as to give the methyl groups their lowest possible number, too.
Step 3 Put the various parts together with commas separating the numbers and hyphens separating the numbers and words. The name of this compound is 3,3-dimethyl-1,4-cyclohexadiene

34. 3) COMPOUNDS CONTAINING HALOGENS AND NITRO GROUPS
The halogens (F, Cl, Br, I) and the nitro group (-NO2) are always named as prefixes in the same way as side chains on hydrocarbons. The prefixes are as follows:

37. 3) COMPOUNDS WITH FUNCTIONAL GROUPS NAMED AS SUFFIXES
(i) General Naming Scheme
The name of every organic molecule containing a functional group whose name appears as a suffix may be thought of as made up of four parts:

38. Base name of acyclic comp.
Name of function
Formula
Prefix
Suffix
Base name of acyclic comp.
Cation
-NR3
Ammonio-
-ammonium
Trialkyl ammonium
Carboxylic acid
-COOH
Carboxy-
-oic acid
Alkanoic acid
Sulphonic acid
-SO2OH
Sulpho-
-sulphonic acid
Alkanesulphonic acid
Ester
-COOR
Alkoxycarbo nyl-
Carbalkoxylate …oate
Alkanecarboxylate
Acid Halide
-COX
Haloformyl-
-oyl halide
Alkanoyl halide
Amide
-CONH2
Carbamoyl-
-amide
Alkanamide
Carbonitrile
-CN
Cyano-
-nitrile
Alkanenitrile
Isonitrile
-NC
Isocyanide-
-carbylamine
alkylcarbylamine

39. Base name of acyclic comp.
Name of function
Formula
Prefix
Suffix
Base name of acyclic comp.
Aldehyde
-COH
Formyl-
-al
alkanal
Ketone
COR
Oxo-
-one
Alkanone
Alcohol
-OH
hydroxy
-ol
Alkanol
Thiol
-SH
Mercapto-
-thiol
Alkanethiol
Amine
-NH2
Amino-
-amine
alkanamine
Imine
=NH
Imino-
-imine
imine
Ether
-OR
alkoxy
Alkoxy alkane
Thioether
-SR
R-thio-
alkoxythio
Alkene
C=C
------
-ene
Alkyne
-CC-
--yne
alkyne

40. A. Choosing the Principal Chain
The Principal Chain is chosen according to the following rules, applied in order:
(a) The chain must contain the (maximum number of) principal functional group(s); then
(b) it must contain the maximum number of double and triple bonds; then
(c) it must be the longest possible carbon chain (the carbons of the -CO2H, -CΞN, -C(=O)H etc. groups are counted when they form part of the principal chain).
B. Naming the Principal Chain
The principal chain is named after the alkane having the same number of carbon atoms, and is modified when unsaturated by the replacement of “ane" by "en(e)", "enyn(e)", "adiene“, etc. The final “e” of the name is omitted before "y" or a vowel (e.g. methaneol becomes methanol).

41. C. Numbering the Principal Chain
The principal chain is numbered according to the following rules, taken in order:
(a) the PFG.'s must be given the lowest possible numbers; then
(b) the double and triple bonds must be given the lowest possible numbers; then
(c) the remaining functional groups and substituents must be given the lowest possible numbers.

43. A. Ethers and Thioethers
(ii) Naming Various Classes of Organic Compounds
A. Ethers and Thioethers
In the naming of ethers as alkyloxy derivatives of alkanes, it is general practice to shorten the names of compounds containing four or less carbons to alkoxy derivatives (i.e., omit thesyllable "-yl-°'), e.g., methyloxy becomes methoxy, ethyloxy becomes ethoxy, but pentyloxy(for CH3CH2CH2CH2CH2O-) is correct. An alternative system for naming ethers (or thioethers) is to name the alkyl groups on oxygen (sulfur) and list them in alphabetical order as separate words before the name "ether" (or sulfide).

44. B. Alcohols and Thiols
(a) -OH or -SH as the principle functional group

45. (b) -OH or -SH as other than the principle functional group

46. Alcohol and Thiol Salts
The salts of alcohols and thiols are most simply named by adding "-ate" after the "-ol" of the name. Alternatively, the alcoholates may be named as alkyloxides (dropping the "yl" syllable for the first four members as in ether naming).

47. C. Acids, Salts of Acids and Acid Anhydrides
Carboxylic acids are named by identifying the longest carbon chain containing the carboxylic acid functional group and using this carbon chain as the stem for the carboxylic acid name. The ending "-anoic acid" is added to the stem to indicate that the compound is a carboxylic acid.

49. Acid anhydrides are named when symmetrical by replacement of the word "acid" by anhydride. When unsymmetrical, the two acid groups are named as separate words in alphabetical order and the word anhydride is added.

50. Acid salts are named by replacing the “ic” ending of the acid name with “ate”.

51. D. Esters
The alkyl (alkenyl etc.) group on oxygen is named as a separate word and is followed by the acid salt name ("-ic acid" becomes "-ate").

52. E. Acid Halides
Acid halides are maned by replacing the "-ic acid" ending of the parent carboxylic acid with"-yl halide”.

53. F. Amides
Primary amides are named by identifying the carboxylic acid from which the amide is derived and replacing the "-ic acid" or "-oic acid" ending of the parent carboxylic acid name with the ending "-amide".
When there are substituents on the N atom, these are named using N-alkyl or N,N-dialkyl as prefixes (note N or N,N are italicised) immediately before the main chain name.

54. G. Nitriles
The nitriles formed from acids with trivial names are named by replacing the “ic acid” ending of the parent carboxylic acid with "-onitrile". Otherwise, "-nitrile" is used as a suffix to the stem name of the parent alkane.

55. H. Aldehydes
Aldehydes formally derived from acids having a trivial name are named by adding "-aldehyde" to the trivial stem ,otherwise the suffix “-al” is used.

57. Derivatives of aldehydes and ketones, e. g
Derivatives of aldehydes and ketones, e.g. oximes or hydrazones are named simply by adding the word oxime etc. after the aldehyde or ketone name.

58. I. Ketones
Ketones are named by adding the suffix "-one" to the stem of the parent carbon chain.

60. J. Amines and Ammonium Salts
The systematic method of naming amines, whereby "-amine" is added to the principal chain name is, in practice, only rarely used and an older method is in common (I.U.P.A.C.accepted) use. Amines are named as derivatives of ammonia. The longest chain attached to the nitrogen atom is named in the usual way for an alkyl group (the carbon attached to the nitrogen is carbon 1). Any other N- substituents are named as N-alkyl, or N,N-di alkyl substituents. The alkyl name for the longest stem is then added to the suffix "amine".

61. Imines are best named systematically
Ammonium Salts are named as alkyl derivatives of inorganic ammonium salts. Note that the N- system is not used and the four alkyl groups attached to N are listed alphabetically.

62. 5) AROMATIC COMPOUNDS
(i) General Notes
The use of numbers to indicate the position of substituents on aromatic rings is supplemented in the case of di substituted derivatives of benzene by the terms:
ortho- abbreviated o- indicating 1,2-disubstitution
meta- abbreviated m- indicating 1,3-disubstitution
para- abbreviated p- indicating 1,4-disubstitution

63. Step 1 Name the compound as a derivative of benzene
Step 1 Name the compound as a derivative of benzene. Thus, the parent name of the compound is benzene.
Step 2 Number the positions of the side chains to get the smallest total. Both are ethyl groups, so both are alphabetically the same, and either could receive the number one. Start with the ethyl on the right and number to the left to give the smaller total.
Step 3 Because the compound is a 1, 3 substituted benzene, you can call it by the meta prefix.
Step 4 Put the name together. The name is 1,3-diethylbenzene or m-diethylbenzene.

64. (ii) Aromatic Hydrocarbons

65. (iii) Substituted Aromatic Compounds
A. Halogen and Nitro- Substituted Aromatics
These are named using halo- or nitro- prefixes before the name of the aromatic hydrocarbon in the usual way.

66. Step 1 Find the parent chain
Step 1 Find the parent chain. The parent chain is a six-membered hydrocarbon. Its name is cyclohexane.
Step 2 Number the side chains. There are two, an ethyl group and a fluorine. Alphabetically ethyl comes first, so it gets the number one. Give the fluorine the number 3, not the number 5.
Step 3 Put the name together. The name of the compound is 1-ethyl-3-fluorocyclohexane.

67. B. Carboxylic Acids and Derivatives
The following list gives the trivial (usually accepted) names for some of the common aromatic acids and derivatives.

68. Carboxylic acid Derivatives
Acid derivatives, esters, anhydrides, amides and nitriles are named in the usual way, replacing "-oic" or "-ic" of the acid name with the appropriate endings.

69. C. Phenols and Thiophenols
Phenols have an –OH group attached directly to an aromatic ring.

70. When the -OH group is not the principal functional group, "hydroxy" is used in the usual way.

71. D. Aldehydes and Ketones
Aldehydes are named by replacing the "-ic" or "-oic" of the acid name by "aldehyde”.

72. Aromatic ketones are named by changing the "ic" or "oic" ending of the acid name corresponding to the acyl group attached to the benzene ring to "-ophenone"

73. Aldehydes and ketones in which the carbonyl group is not directly attached to the aromatic ring are named using the corresponding group name for the aromatic system as a prefix.

74. E. Sulfonic Acids and Sulfonic Acid Derivatives
Sulfonic acids are named by adding the suffix "-sulfonic acid".

75. Sulfonic Acid Derivatives
Sulfonic Acid Derivatives. Derivatives of sulfonic acids (esters, amides and sulfonic acid chlorides) are named by analogy with carboxylic acids.

76. F. Aromatic Amines

77. The remaining aromatic amines are named as derivatives of these or (in the presence of more important functional groups) as "amino-" derivatives, or as "phenylamines".

78. Ammonium Salts
These are named by changing the "-e" of the special names to “-ium".

79. Acyl Derivatives (Amides)
Simple acyl derivatives are named by adding the trivial acid name stem to "-anilide" etc.
G. Diazonium Ions (ArN2+)
These are named in an analogous fashion to sulfonic acids; the syllable "-diazonium" is added to the aromatic name.

80. 6. RADICOFUNCTIONAL NAMING
An alternate system of naming, which is still very common in many textbooks, consists of naming the alkyl or aryl groups attached to a certain functional group as separate words followed by the functional group name. The alternative naming of ethers and amines is a remnant of this system. The following examples suffice to illustrate the system.