14024052 iupac nomenclature exercises in organic chemistry

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Updated on 22nd Nov, 2009 and going to be updated frequently. For recent updates andother files, visit

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IUPAC NOMENCLATURE EXERCISES IN ORGANIC CHEMISTRY

Propose IUPAC names for the following compoundsNote: Key with possible explanation is given at the end.

1)C2H5

CH3

OR CH3

CHCH

CH2CH3

C2H5

CH3

2) ORCH3

CHCH

CHCH

CH2

CH3

CH3

CH3 CH3

CH2CH2

CH3

3) ORCH3

CHCH2

CHCH

CH2

CH3

CH3

CH2CH

CH3

CH3

CH3

4) OR CH3CH2

CHCH

CH2CH2

CH2CH2

CHCH3

CH3CH3

CH3

5) OR

CH3C

CHCH2

CH2

CH3

CH3

CH3

CH2CH3

6) ORCH3

CH2CH2

CH2CH2

CHCH

CH2CH2

CH2CH3

CH2

CHCHCH3

CH2

CH3

CH3

CH3

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7) 8)

9) 10)

11) 12)

13) 14)

15) 16)

17) 18)

19) 20)

21) C 22)

23) 24)

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25) 26)

27) 28)

29) 30)

KEY WITH EXPLANATION

1)

C2H5

CH3

3,4-Dimethylhexane and not 2-Ethyl-3-methylpentane

Explanation:* This is the common mistake observed. The longest chain is NOT always expected to bearranged linearly. The parent chain may be represented zigzag. The condition is the carbons inthe chain must be continuous. In this case, longest chain contains six carbons continuously asshown below.

C2H5

CH3

2 1

3 4 56 OR

CH2-CH3

CH3

2 1

3 45

6

2)

2,3,5-Trimethyl-4-propylheptane

Explanation:* If chains of equal length are competing for selection as parent chain in a saturatedbranched acyclic hydrocarbon, then the choice goes to the chain which has the greatestnumber of side chains.

3)2,5-Dimethyl-4-(2-methylpropyl)heptane

4-Isobutyl-2,5-dimethylheptane

or

Explanation:* In this case, The chain whose side chains have the lowest-numbered locants is taken asthe main chain.* Note the two versions. Isobutyl radical is also a valid name and it can also be named as 2-

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methylpropyl.* Following names may be used for the given unsubstituted radicals only.

CH3

CH

CH3

CH3

CH

CH3

CH2

CH2

Isopropyl Isopentyl

CH3

CH

CH3

CH2 CH3 C

CH3

CH2

CH3

Isobutyl Neopentyl

CH2

CH

CH3

CH3

CH3 CH2 C

CH3

CH3

sec-Butyl tert-Pentyl

CH3

CCH3

CH3

CH3

CH

CH3

CH2

CH2 CH2

tert-Butyl Isohexyl

4)2,7,8-Trimethyldecane and not 3,4,9-Trimethyldecane

even though 3+4+9 = 16 --- least sum

whereas2+7+8 = 17 --- first locant is least

Explanation* When series of locants containing the same number of terms are compared term by term,that series is "lowest" which contains the lowest number on the occasion of the first differ-ence.* Actually the so called “Least Sum Rule” is the special case of above “Rule of First Differ-ence”. And incidentally, in most of the simple cases we still use “Least Sum Rule”. But thisbecomes tedious when there are more than two substituents and where the actual rule willcome to the surface. (If you don’t use “least sum rule” neglect this statement.)

5)3-Ethyl-2,2-dimethylhexane

Explanation:* If two or more side chains of different nature are present, they are cited in alphabetical order.* In case of simple radicals, they are alphabetized based on the first letter in the name of simpleradical without multiplying prefixes.

For example, compare ‘e’ in ethyl with ‘m’ methyl, and not ‘e’ in ethyl with ‘d’ in dimethyl.BUT CONSIDER THE NEXT PROBLEM.

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6)

6-(1,2-Dimethylbutyl)-5-ethylundecane

Explanation:* The name of a complex radical is considered to begin with the first letter of its completename.* In this case, “dimethyl” is included in the radical name (Note: “di”does not indicate twomethylbutyl side chains).* Hence dimethylbutyl (as complete single substituent) is alphabetized under "d".

7)3-Ethyl-4-methylhexane

Explanation:* If two or more side chains are in equivalent positions, the one to be assigned the lowernumber is that cited first in the name.* Previously, the less complex side chain is assigned the least number, which is discarded now.

8)

4-Ethyl-3-methylheptane

Explanation:* In this case, ethyl and methyl groups are not at equivalent positions. Hence according to“Rule of First Difference”, methyl is given the lowest number.

9)

7-(1-methylbutyl)-9-(2-methylbutyl)pentadecane

Explanation:* In this case the names of complex radicals are composed of identical words. Hence priorityis given to that radical which contains the lowest locant at the first cited point of difference inthe radical.

10)5,5-Bis(1,2-dimethylpropyl)nonane

5,5-Bis-1',2'-dimethylpropyl)nonaneOR

Explanation:* Multiplying prefixes like bis-, tris-, tetrakis-, pentakis- etc., are used to indicate more thanone identical side chain which contains terms like bi-, tri-, tetra- etc., in its name.* The side chain may be enclosed in parentheses

or carbon atoms in the side chains may be indicated by primed numbers.

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11)

4,6-Di(propan-2-yl)nonane

4,6-DiisopropylnonaneOR

Explanation:* Note the use of “propan-2-yl” for isopropyl radical.

12)

5-tert-Butyl-6-isobutyldecane

Explanation:* The prefixes - “tert” or “sec” are not taken into consideration for deriving alphabeticalpriorities. But “iso” is considered to be the part of radical name and important in decidingalphabetical priority.* In this case, tert-Butyl is alphabetized under “B” whereas isobutyl under “i”

13)

5-tert-Butyl-6-sec-butyldecane

Explanation:* tert-Butyl group is given priority over sec-butyl group. (Why?)

14) (3E)-7-Methyloct-3-ene

Explanation:* Double bond must be given priority (and hence lowest number) over “alkyl” groups.* Only the lower locant of the double bond ( i.e., 3) is cited as the locants of double bond differby unity (i.e., 3,4).* It is in ‘E’(Entgegen) geometrical configuration. The groups with higher priority are on theopposite sides of double bond.

H

H

1

12

2

* But the following is in ‘Z’(Zusammen) configuration i.e., groups with higher priorities areon the same side of double bond.

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(3Z)-7-Methyloct-3-eneH

H

11

2

2

Additional information:E-Z Notation:Following procedure can be adopted while arriving at the stereochemistry around the doublebond and can be denoted by E or Z descriptors. (Remember, if any of the doubly bondedcarbon is attached to two similar groups, then there is no need of giving E-Z descriptors.)

* Determine the higher priority group on each end of the double bond. If the higher prioritygroups are:

on opposite sides of double bond: E (entgegen = opposite)on the same side of double bond: Z (zusammen = together)

The priorities are assigned by following Cahn-Ingold-Prelog sequence rules.* Rank the atoms directly attached to the olefinic carbon according to their atomic number.High priority is given to the atom with higher atomic number.* In case of different isotopes of same element, then higher priority is given to the isotope withhigher atomic mass. (Eg., D>H, C13>C12)* If the atoms are still identical, examine the next atoms along the chain until a “first point ofdifference” is found. This is done by making a list of atoms linked directly to the atom. Eachlist is arranged in order of decreasing atomic number. Then the higher priority is given to thelist which contain atom with higher atomic number at first point of difference.Eg., Examine the lists of atoms directly linked to the highlighted carbons in the followingcompound, (2Z)-2-tert-Butyl-3-methylpent-2-en-1-ol.

CH3

C C

CH2

C

CH2 OH

CH3

CH3

CH3

CH3

C,H,H

H,H,H

O,H,H

C,C,C

*

*

*

*

* Multiple bonds are counted as multiples of that same atom i.e., each - bond is treated as ifit were another - bond to that type of atom.Eg.,

C C CH3 C C CH3

C

C

C

C

is equivalent to

C,C,C

* *

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C

CH3

O

* is equivalent to C CH3

O

O C

*

O,O,C

15) (2E,4E)-3-Methylhexa-2,4-diene

Explanation:* It is a diene. The positions of two double bonds are indicated by 2,4. At each double bondthe configurations are indicated by 2E,4E.* Starting from either side of the chain, the double bonds are getting same numbers. Hencethe carbons on the main chain are numbered such that methyl group is given the leastnumber.

16)(4E)-4-Methylhept-4-en-2-yne

Explanation:* The triple bond is given the lowest number.* Another common mistake observed is, students name this compound as (4E)-4-Methylhept-3-en-5-yne, which is wrong. Remember the ‘Rule of first point of difference’.In this case, the carbons are counted such that triple bond gets least number. Howeverconsider the next problem.

17)(2Z)-4-Methylhept-2-en-5-yne

Explanation:* Double bond is given the lowest number when both double and triple bonds are at equiva-lent positions.

18)

(3Z)-3,4-Diethylhexa-1,3-dien-5-yne

Explanation:* When two chains of equal length are competing, then the chain with maximum number ofdouble and triple bonds is selected as main chain.* Observe the notation (3Z). There is no need to assign E-Z descriptor for first doublebond.* In this case also, double bond is given more priority while numbering the chain.

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19)

(4Z)-4-Ethenyl-5-ethynyloct-4-ene

Ethenyl group(also named as vinyl group)

Ethynyl group

Explanation:* In this case, longest chain contains eight carbons and it should be taken as the parentchain irrespective of whether it contains maximum number of unsaturations or not.* Selection of chain containing maximum number of unsaturated bonds as main chain (oldIUPAC), even though there is a longer chain containing less number of double or triplebonds, is not followed now.

Additional information:* The names of univalent radicals derived from unsaturated acyclic hydrocarbons have theendings “-enyl”, “-ynyl”, “-dienyl”, “-diynyl” etc., and the positions of double and triplebonds must be indicated where ever necessary.

CH2 CH vinyl or ethenyl

CH2

CHCH2

allyl or prop-2-en-1-yl

CH3

CHCH prop-1-en-1-yl

CH3

CCH2

isopropenyl or prop-1-en-2-yl or 1-methylvinyl

CH C Ethynyl

CH C CH2 Prop-2-yn-1-yl

CH3 C C Prop-1-yn-1-yl

20) 3-methylidene-5-(prop-1-yn-1-yl)decane

Explanation:* The names of divalent radicals, formed by removing two hydrogens from a carbon atomof acyclic hydrocarbon end with “-idene”.

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CH2 methylidene or methylene

CH3

CHEthylidene

CH2 Cethenylidene

or vinylidene

CH3

CH2CH

propan-1-ylideneor

propylidene

CH3

C

CH3 propan-2-ylidene or

Isopropylidene

21) C4-ethenylideneheptane

or 4-vinyledeneheptane

Note: It is a cumulene. The carbon shown is “sp” hybridized.

22) Hexylcyclopentane

1-Cyclopentylhexaneor

Explanation:* In the first name, cyclopentane is given more priority, eventhough the straight chaincontains more carbons, and taken as root word. This is according to the rule -“cycles aresenior to acycles”.

* In the second case, hexane is taken as root word as it contains more number of carbonsthan cyclopentane. This type of naming was actually suggested in 1979 recommendationsand can be stated as follows.

“a hydrocarbon containing a small cyclic nucleus attached to a long chain is generallynamed as a derivative of the acyclic hydrocarbon; and a hydrocarbon containing a smallgroup attached to a large cyclic nucleus is generally named as a derivative of the cyclichydrocarbon.”

* Most of the older textbooks follow the second convention.23)

1-ethyl-2-methylcyclohexane

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24)

ethenylcyclobutane

25) methylidenecyclohexane

26) 1-ethenyl-3-ethylcyclopentane

What about ?

It is (3Z)-1-ethenyl-3-ethylidenecyclopentane

27) (1E)-prop-1-en-1-ylcyclopropane

28) cyclopentene

29) cyclopenta-1,3-diene

30) (1E,3Z,5E,7Z,9Z)-cyclodeca-1,3,5,7,9-pentaene1

23

45 6 7

8

910

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14024052 iupac nomenclature exercises in organic chemistry

Documents

common mistake observed

aditya vardhan adichemadi

higher atomic number

higher priority

parent chain

ha em

root word

va di