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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5574_Библиотеки_им_академика_М_И_Перельмана.pdf
When carbon (C), oxygen (O) and hydrogen
(H) atoms bond in a certain way to form
sugar, the resulting compound has a sweet
taste. The sweetness resides neither in
the C, nor in the O, nor in the H; it resides
in the pattern that emerges from their
interaction. It is an emergent property.
Moreover, it is not a property of the chemi-
cal bonds. It is a sensory experience that
arises when the sugar molecules interact
with the chemistry of our taste buds, which
2
2.1 Introduction, 2.2 IUPAC Nomenclature of Organic compounds, 2.3 General Rules of IUPAC Systems, 2.4 Nomenclature of Hydrocarbons,
2.4.1 Nomenclature of Saturated Branched Chain Acyclic Hydrocarbon, 2.4.2 Nomenclature of Unsaturated Hydrocarbons, 2.4.3 Nomenclature of Cyclic (Alicyclic) Hydrocarbons, 2.4.4 Nomenclature of Polycyclic Hydrocarbons, 2.5 IUPAC Nomenclature of Compounds Containing
One Functional Group, Multiple Bonds and Substituent, 2.6 Nomenclature of Polyfunctional Compounds, 2.6.1 Some Additional Rules for
Solving Complex Compounds, 2.6.2 Specific Classes of Organic Compounds, 2.7 Nomenclature of Substituted Alicyclic Compounds Having
Some Functional Group Along with Other Substituents, 2.8 Nomenclature of Aromatic Compounds
in turns causes a set of neurons to fire in a
certain way. The experience of sweetness
emerges from that neural activity.
–Fritjof Capra
Chapter Outline
2.1 INTRODUCTION
The simplest organic compounds are hydrocarbons which are made up of carbon and hydrogen. All other
compounds can be considered to have been derived from hydrocarbons by the replacement of one or more
hydrogen atoms by other atoms or groups. Thus organic chemistry can be dened as the chemistry of
hydrocarbons and their derivatives.
For the sake of convenience and in order to study them systematically,
the organic compounds have mainly been grouped into two classes: (1) open-chain or acyclic or aliphatic
compounds and (2) closed-chain or ring compounds.
92
Organic compounds
Open chain or acyclic compounds
(butane, ethanol, ethanoic acid, etc.)
Closed chain or cyclic
compounds
Heterocyclic
compounds
Homocyclic or carbocyclic
compounds
Aromatic compounds or benzenoids
(benzene, phenol, benzoic acid, etc.)
[follow (4n + 2)π electron rule or Huckel rule]
Alicyclic compounds
(Cyclopropane, cyclohexane, etc.)
Aromatic heterocyclic compounds
or non-benzenoid heterocycic compounds
(furan, thoiphene, pyridine, etc.)
[These also follow Huckel rule]
Nonaromatic
heterocyclic
compounds
(THF, dioxane
piperidine, etc.)
PhArmAceuTicAl OrgAnic chemisTry
These have been described briey as follows:
There are four types of carbon atoms:
1. Primary (1º) carbon atom, which is bonded to either one more carbon atom or to none.
2. secondary (2º) carbon atom, which is bonded to two other carbon atoms.
3. Tertiary (3º) carbon atom, which is bonded to three other carbon atoms.
4. Quaternary (4º) carbon atom, which is bonded to four other carbon atoms.
The hydrogens attached to 1º, 2º and 3º carbon atoms are called 1º, 2º and 3º hydrogen atoms,
respectively.
The 1º, 2º, 3º and 4º carbon atoms are illustrated below:
2.2 IUPAC NOMENCLATURE OF ORGANIC COMPOUNDS
The main aim of nomenclature is to identify a chemical species. The systematic nomenclature must always
lead to an unambiguous name. Thus, it requires a system of principles and rules so that only one name can
be given to a particular compound having a denite structure. At the same time it clearly directs in writing
one and only one molecular structure for a given name.
c h A P T e r 2 u nomenclature of Organic compounds
There are traditional names in addition to systematic names. These traditional names can be trivial or
semisystematic.
A trivial name has no systematic sense, i.e. glucose. A semisystematic name has at least one systematic
part, i.e. acetone (one), ethylene (ene).
According to the iuPAc rules (1979) and its latest recommendation, these names may be used and for the
most part preferred to fully systematic if they meet the requirements of utility and precision.
For example, the name acetic acid for ch3cOOh is not only allowed but preferred over its systematic
name, i.e. ethanoic acid.
2.3 GENERAL RULES OF IUPAC SYSTEM
The basic rules of iuPAc system with latest amendments, with suitable examples, are illustrated below:
1. The longest possible continuous chain of carbon atoms that must include the carbon atom carrying
the functional group and the maximum number of double and triple bonds is located and the word
root corresponding to it is noted. This is called principal chain (in case of alkanes the longest possible
chain is selected as alkanes do not contain any functional group).
93
C
1
C
2
C
3
C
4
C
5
C
6
C
7
C
8
C
9
C
10
Meth- C
Eth- C
Prop- C
But(a)- C
Pent(a)- C
Hex(a)- C
Hept(a)- C
Oct(a)- C
Non(a)- C
Dec(a)- C
11
12
20
21
22
30
31
40
50
100
Undec(a)Dodec(a)Icos(a)Henicos(a)Docos(a)Triacont(a)Hentricont(a)Tetracont(a)Peracont(a)-
Hect(a)
For example, the principal chain and the corresponding word root is shown below:
The principal chain contains ve carbon atoms as it contains the functional group as well as the double
bond, and therefore, the word root is pent.
Extra ‘a’ given in parenthesis is used only if the primary sufx to be added to the root word does not begin
with ‘e’ or ‘y’. in general, the root word for a principal chain is ‘alk’.
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PhArmAceuTicAl OrgAnic chemisTry
2. A primary sufx is added to the word root to designate the saturated or unsaturated nature of the prin-
cipal chain. The three basic primary sufxes are: ‘ane’ for saturated principal chain; ‘ene’ for unsaturated principal chain with one double bond and ‘diene’ for two double bonds; ‘-yne’ for unsaturated
principal chain with one triple bond and ‘diyne’ for two triple bonds.
The locants (positional numbers) of the primary sufxes are placed immediately before the name of
the primary sufx. Hyphens are used to separate locants form the sufxes. Commas are used to separate
locants.
The following examples illustrate the use of primary sufx after the word roots.
Pent - 2 - ene
(word root) (locant) (primary suffix)
Hex - 2 - yne
(word root) (locant) (primary suffix)
Buta - 1,3 - diene
(word root) (locant) (primary suffix)
3. A secondary sufx is added after the primary sufx to indicate the nature of functional group present
in the given organic compound. The positional number (locant) of the secondary sufx (the functional
group) is placed immediately before the secondary sufx. For example,
CH3CH2CN Propanenitrile CH3CH=CHCH2–CN Pent-3-ene nitrile
1. Carboxylic acid –COOH -oic acid
2. Esters –COOR Alkyl….oate
3. Acid chlorides –COCl -oly chloride
4. Acid amides –CONH
5. Acid anhydride
6. Aldehyde –CHO -al
7. Ketones
8. Nitriles –CN -nitrile
9. Isocyanide
–N≡C
2
O
C
O
C
O
C = O
-amide
Anhydride
-one
Isocyanide
Contd…
C H A P T E R 2 u Nomenclature of Organic Compounds
CH3– (or Me)
Methyl
CH3–CH2– (or Et)
Ethyl
CH3–CH2–CH2– (or n-Pr)
n-Propyl Propyl
Isopropyl
or 1-Methyl ethyl
(or Pr)
n-Butyl
or Butyl
sec-Butyl
or 1-Methyl propyl
S. no. Class of the organic compound Functional group Secondary sufx
10. Thiol –SH -thiol
11. Alcohols –OH -ol
12. Amines –NH
2
Amine
4. Aprimaryprex,cyclo is used immediately before the word root in case of alicyclic (but not aro-
matic)compounds.Intheabsenceofthisprex,thecompoundisassumed.Forexample,
(cyclo primary suffix, hex word root, ane primary suffix)
5. Secondary prexesareadded beforethe wordroot(or beforetheprimary prexin caseofcarbo-
cyclic or alicyclic compounds) in alphabetical order to denote the side chains or substituent groups.
Apartfromalkylgroupsomeothergrouplikeuoro(–F),chloro(–Cl),bromo(–Br),iodo(–I),nitro
(–NO2),nitroso(–NO),alkoxy(–OR),etc.,arealwaystreatedassubstituent groups;moreover,other
functionalgroups arealso treatedas substituentgroups in caseof polyfunctionalcompounds. For
example,
95
Thevarioustypesofsubstituents(secondaryprexes)containingcarbonatomsareasfollows:
a. Alkyl groups are obtained by removal of a hydrogen atom from the molecule of an alkane. Their
general formula is (C
) and are usually represented by the letter ‘R’. Their names are obtained
nH2n+1
byreplacingtheterminal‘e’fromthenameofthecorrespondingalkanebythesufx,i.e.alkane–
e+yl=alkyl.Forexample,
Note: Only isopropyl and secondary propyl radicals are the same.
96
Isobutyl
or 2-Methyl propyl
tert-Butyl
or 1,1-Dimethyl ethyl
Neopentyl
or 2,2-Dimethyl propyl
PhArmAceuTicAl OrgAnic chemisTry
b. Alkenyl and alkynyl groups
i. Alkenyl radicals are obtained by removing one hydrogen form an alkene (Alkene – e + yl =
Alkenyl).
ii. The atom with free valence is given the locant ‘1’ and the position of double bond is also
indicated also locant including ‘1’ for free valence must be cited.
CH
C3H
C4H
C4H
CH
CH
CH
CH Vinyl Ethenyl
2
H
H
2
1
H
2
2
C
H
C2H C
C1H
1
H
Allyl Prop-2-ene-1-yl
– But-1-ene-1-yl
2
– But-2-ene-1-yl
– Methylidene
– Ethylidine
– Propylidine
C2H C
2
3
C
3
3
C
3
2
CH
3
CH2 CH
3
CH3 C CH
CH
2
CH
CH
3 2 1
CH C
4 3 2 1
CH C CH2 CH2
4 3 2 1
CH3 CH2 C C
c. A substituted substituent or a complex substituent: When a substituent itself is substituted, all the
CH CH
C CH
3
– Isopropylidine
– Prop-2-enylidine
– Prop-2-ynyldine
C – Ethynyl
CH2
Propargyl Prop-2-yn-1-yl
– But-3-yn-1-yl
– But-1-yn-1-yl
subsidiary substituents are named as prexes. The substituent having the subsidiary substituents
c h A P T e r 2 u nomenclature of Organic compounds
4-Chlorocyclohexane-1-ol
is regarded as a principal substituent. The point of attachment of the complex substituent with the
main chain has the lowest permissible locant. For example,
–CH2OH –CH2–C≡N –CH2–CHO –CH2COOH –CH2CH2Cl
Hydroxymethyl Cyanomethyl Formyl methyl Carboxymethyl 2-Chloroethyl
Thus a complete IUPAC name of an organic compound consists of secondary prex + primary prex +
word root + primary sufx + secondary sufx. For example:
2.4 NOMENCLATURE OF HYDROCARBONS
2.4.1 Nomenclature of Saturated Branched Chain Acyclic Hydrocarbon
This type of acyclic hydrocarbon is named by prexing the designations of the side chains (alkyl groups)
groups to the name of the longest chain of the formula. The following rules are observed. certain
semisystematic names are retained.
97
1. The prex iso is used for a branched alkane containing a methyl group and a hydrogen
atom at the second carbon atom of the chain.
2. The prex neo is used for a branched chain alkane containing quaternary carbon atom,
i.e. a carbon atom directly linked to four carbon atoms.
The longest possible continuous chain of carbon atoms is selected and the compound
is considered as the derivative of the corresponding alkane. The chain so selected is called a parent chain.
Any alkyl group attached to the parent chain is called side chain or substituent. For example,
98
PhArmAceuTicAl OrgAnic chemisTry
if a molecule contains two or more continuous chains of equal length, the chain which is highly substituted
i.e. contains maximum number of substituents is selected as the parent chain.
The parent chain has three substituents whereas the other equivalent length chain has two substituents.
3. The selected longest chain is numbered by arabic numerals 1, 2, 3, 4…… and
so on from that end which gives lower number to be carbon-carrying substituent.
4. When two or more different alkyl groups are present on the
principal chain, each alkyl group prexed by its positional number is arranged in alphabetical order
(irrespective of its positional number) before the word root or the name of the parent alkane. For
example,
When a series of alkyl radicals (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 rst difference. This principle
is applied irrespective of the nature of the alkyl radical prex di, tri or tetra, etc., is used to indicate that the
total number of identical substituents is two, three or four, respectively. For example,
c h A P T e r 2 u nomenclature of Organic compounds
6
3,4,9-Trimethyl decane
(not 2,7,8-trimethyl decane lowest sum rule is not applicable here)
When two or more different alkyl groups are present at equivalent positions on the parent chain, the lower
number is given to that which comes rst in the alphabetical order. For example,
99
so the correct name is: 3-ethyl-4-methyl hexane.
The name of simple alkyl radicals is rst alphabetized and the multiplying prexes are then inserted.
For example,
in case the substituent of the parent chain has sub-branching, the substituent is named as a derivative of
the longest chain present in the substituent. in such case, the numbering of the carbon chain of the substituent is started from the carbon atoms that is directly linked to the parent chain, i.e. the carbon atoms with
free valency and it is given number 1. The name of the substituents is nally enclosed in parenthesis. For
example,
100
5-(1,2-Dimethylpropyl)-nonane
PhArmAceuTicAl OrgAnic chemisTry
The name of a complex alkyl radical is considered to begin with the rst letter of its complete name.
For example,
(here dimethyl propyl is a complete substituent which starts with ‘d’ and methyl ethyl is also a complete
substituent which starts with ‘m’ and hence the above alphabetical order is being considered in the above
example.)
The presence of identical complex radicals each containing two or more identical radicals as side chains
in the same or different positions may be indicated by approximately multiplying prex bis-, tris-, tetrakis-,
pentakis-, etc. The complete expression denoting such as a side chain may be enclosed in parenthesis.
CH
3
C — C — CH2CH
H
H3C — CH — CH — CH2 — C — CH2 — CH2 — CH2 — CH
1 2 4 5 6 7 8 9
5,5-Bis (1,1-dimethyl propyl)-3-ethyl-2-methyl nonane
3
3
C2H
H3C — C — CH2CH
5
CH
3
3
3
3