14024052 Iupac Nomenclature Exercises In Organic Chemistry

This document is going to be updated again. You are requested to add this to your favourites and check again. This document is updated on 11th Apr, 2009. For recent updates, join the following group http://groups.google.com/group/adichemadi Prepared by V. Aditya vardhan adichemadi(at)gmail.com WARANGAL BEST IUPAC NOMENCLATURE EXERCISES IN ORGANIC CHEMISTRY C2H 5 1) CH3 2) 3) 4) 5) ad V.A ic D he IT m YA ad V i @ AR gm DH ai AN l.c om C2H5 CH Propose IUPAC names for the following compounds Note: Key with possible explanation is given at the end. OR CH2 H3C CH CH3 CH3 CH3 CH CH3 CH H3C CH3 OR CH CH CH2 CH3

H2C CH2 CH3 CH3 CH H3C CH2 CH3 OR CH CH CH2 CH3 H2 C CH3 CH CH3 CH3 CH CH3 CH OR H3 C CH2 CH2 CH2 CH CH2 CH2 CH3 CH3 H3C C CH3 CH2 CH CH2 CH3

OR H3C CH2 H3C

Prepared by V. Aditya vardhan adichemadi(at)gmail.com CH3 H3C CH CH CH2 CH2 CH CH2 H3C CH2 CH2 CH3 CH3 WARANGAL 6) OR H3C CH2 CH2 CH2 CH2 CH 7) 8) 9) 10) 11) 12) 13) 14) ad V.A ic D he IT m YA ad V i @ AR gm DH ai AN l.c om

Prepared by V. Aditya vardhan adichemadi(at)gmail.com WARANGAL 15) 16) 17) 18) 19) 1) C2H5 CH3 Explanation: * This is the common mistake observed. The longest chain is not always expected to be arranged linearly. The parent chain may be represented zig zag. The condition is that carbons in the chain must be continuous. In this case, longest chain contains six carbons continuously as shown below. C2H5 2 1 2) 2,3,5-Trimethyl-4-propylheptane Explanation: * If chains of equal length are competing for selection as parent chain in a saturated branched acyclic hydrocarbon, then the choice goes to the chain which has the greatest number of side chains. ad V.A ic D he IT m YA ad V i @ AR gm DH ai AN l.c om KEY WITH EXPLANATION 3,4-Dimethylhexane and not 2-Ethyl-3-methylpentane CH 2 -CH 3 4 5 OR CH3 3 6 CH3

Prepared by V. Aditya vardhan adichemadi(at)gmail.com WARANGAL 3) 2,5-Dimethyl-4-(2-methylpropyl)heptane or 4-Isobutyl-2,5-dimethylheptane Explanation: * In this case, The chain whose side chains have the lowest-numbered locants is taken as the main chain. * Note the two versions. Isobutyl radical is also a valid name and it can be named as 2methylpropyl. * Following names may be used for the given unsubstituted radicals only. H3C H3C CH Isopropyl Isobutyl sec-Butyl tert-Butyl 4) 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 difference. * Actually the so called “Least Sum Rule” is the special case of above “Rule of First Difference”. And incidentally, in most of the simple cases we still use “Least Sum Rule”. But this becomes tedious when there are more than two substituents and where the actual rule will come to the surface. (If you don’t use “least sum rule” neglect this statement.) ad V.A ic D he IT m YA ad V i @ AR gm DH ai AN l.c om Isopentyl CH CH2 H3C H3C H3C CH2 CH3 C CH CH2 Neopentyl H3C CH2 H3C CH3 CH3 CH3 C H2C CH tert-Pentyl

H3C CH2 H3C CH3 CH3 C H3C H3C Isohexyl CH CH2 CH3 H3C CH2 CH2 2,7,8-Trimethyldecane and not 3,4,9-Trimethyldecane even though 3+4+9 = 16 --- least sum whereas 2+7+8 = 17 --- first locant is least

Prepared by V. Aditya vardhan adichemadi(at)gmail.com WARANGAL 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 simple radical without multiplying prefixes. For example, compare ethyl with methyl, and not ethyl with dimethyl. BUT CONSIDER THE NEXT PROBLEM. 6) Explanation: * The name of a complex radical is considered to begin with the first letter of its complete name. * In this case, “dimethyl” is included in the radical name (Note: “di”does not indicate two methylbutyl side chains). * Hence dimethylbutyl (as complete single substituent) is alphabetized under "d". 7) Explanation: * If two or more side chains are in equivalent positions, the one to be assigned the lower number is that cited first in the name. * Previously, the less complex side chain is assigned the least number. This is now discarded. 8) 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 priority is given to that radical which contains the lowest locant at the first cited point of difference in the radical. ad V.A ic D he IT m YA ad V i @ AR gm DH ai AN l.c om 6-(1,2-Dimethylbutyl)-5-ethylundecane 3-Ethyl-4-methylhexane 4-Ethyl-3-methylheptane

Prepared by V. Aditya vardhan adichemadi(at)gmail.com WARANGAL 10) 5,5-Bis(1,2-dimethylpropyl)nonane OR 5,5-Bis-1',2'-dimethylpropyl)nonane Explanation: * Multiplying prefixes like bis-, tris-, tetrakis-, pentakis- etc., are used to indicate more than one 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. 11) Explanation: * Note the use of “propan-2-yl” for isopropyl radical. 12) Explanation: * The prefixes - “tert” or “sec” are not taken into consideration for deriving alphabetical priorities. But “iso” is considered to be the part of radical name and important in deciding alphabetical priority. * In this case, tert-Butyl is alphabetized under “B” whereas isobutyl under “i” 13) Explanation: * tert-Butyl group is given priority over sec-butyl group. (Why?) 14) (3E)-7-Methyloct-3-ene Explanation: * Double bond “alkyl” groups. * Only the the locants of double bond geometrical configuration. sides of double bond.

must be given priority (and hence lowest number) over lower locant of the double bond ( i.e., 3) is cited as differ by unity (i.e., 3,4). * It is in ‘E’(Entgegen) The groups with higher priority are on the opposite

ad V.A ic D he IT m YA ad V i @ AR gm DH ai AN l.c om 4,6-Diisopropylnonane OR 4,6-Di(propan-2-yl)nonane 5-tert-Butyl-6-isobutyldecane 5-tert-Butyl-6-sec-butyldecane

Prepared by V. Aditya vardhan adichemadi(at)gmail.com WARANGAL 2 1 H H 2 1 * But the following is in ‘Z’(Zusammen) configuration i.e., groups with higher priorities are on the same side of double bond. 2 2 H H 1 Additional information: E-Z Notation: Following procedure can be adopted while arriving at the stereochemistry around the double bond and can be denoted by E or Z descriptors. (Remember, if any of the doubly bonded carbon 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 priority groups 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 with higher atomic mass. (Eg., D>H, C13>C12) * If the atoms are still identical, examine the next atoms along the chain until a “first point of difference” is found. This is done by making a list of atoms linked directly to the atom. Each list is arranged in order of decreasing atomic number. Then the higher priority is given to the list 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 following compound, (2Z)-2-tert-Butyl-3-methylpent-2-en-1-ol. C,H,H H3C O,H,H 2 * Multiple bonds are counted as multiples of that same atom i.e., each  - bond is treated as if it were another  bond to that type of atom. Eg., ad V.A ic D he IT m YA ad V i @ AR gm DH ai AN l.c om 1 (3Z)-7-Methyloct-3-ene * CH * C * CH2 OH C C H3 * C H3C C,C,C CH3 CH3 H,H,H

C C C C CH3 * C C CH3 is equivalent to C* C C,C,C O C* CH3 OC is equivalent to C* O CH3 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 bond the configurations are indicated by 2E,4E. * Starting from either side of the chain, the double bonds are getting same numbers. Hence the carbons on the main chain are numbered such that methyl group is given the least number. 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)-4Methylhept-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. However consider 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 equivalent 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 of double and triple bonds is selected as main chain. * Observe the notation (3Z). There is no need to assign E-Z descriptor for first double bond. * In this case also, double bond is given more priority while numbering the chain.

19) Ethenyl group (4Z)-4-Ethenyl-5-ethynyloct-4-ene Ethynyl group (also named as vinyl group) Explanation: * In this case, longest chain contains eight carbons and it should be taken as the parent chain irrespective of whether it contains maximum number of unsaturations or not. * Selection of chain containing maximum number of unsaturated bonds as main chain (old IUPAC), even though there is a longer chain containing less number of double or triple bonds as in this case, is not followed now. H2C CH vinyl or ethenyl CH H2C CH2 allyl or prop-2-en-1-yl CH H3C CH prop-1-en-1-yl C H3C CH2 isopropenyl or prop-1-en-2-yl or 1-methylvinyl (2Z,4E)-4-[(1E)-prop-1-en-1-yl]hepta-2,4-diene (2E)-4-[(1E)-prop-1-en-1-yl]hepta-2,4-diene