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UNIT 1 BONDING, FUNCTIONAL
GROUP CLASSIF.ICATION AND
NOMENCLATURE
Structure
1.1 Introduction Objectives 1.2 The Covalent Bond 1.3 Structural Formulas 1.4 Orbital Hybridisation sp3-Hybrldisation s&Hybrldisatlon sp-Hybridisation
1.5 Functional Group Classification
1.6 Nomenclature of Organic Compounds 1.7 Summary 1.8 Terminal Questions 1.9 Answers
1. INTRODUCTION
Organic Chemistry is a highly organised discipline. It is the study of the relationship between the structures of molecules and their reactions. We will begin our study with the type of bonding and structural aspects of the molecules. You are already familiar from Unit 3, Block 1 of the Atoms and Molqcules course that the compounds can be broadly divided into two classes, ionic and',covalent. Ionic compounds are composed of positively and negatively charged ion; which are held together by electrostatic forces. Since ions can be regarded as spheres having symmetrical distribution of charge, no particular direction can be assigned to such type of bonding. For example, in NaCl lattice, N a + and C1- ions are held together by electrostatic forces; no N a + ion can be regarded as bonded to a particular C1- ion. In other words, there is no such entity which can be called as NaCl molecule. In fact, the electrostatic forces operate between a particular ion (Na') and all its neighbouring ions (Cl-) of opposite charge. On the other hand, in covalent compounds, mdecules are the structural units. In contrast-to the ionic compounds, in covalent compounds, the molecules are formed by the sharing o f electron pair(s) between the constituent atoms. The bonds formed by' sharing af pair@) of electrons are called covalent bonds. Since in organic compounds, the bonds forrhed by carbon atom are covalent in nature, we will study some features of the covalent bonding in detail. We will then explain shapes of molecules using the concept of hybridisation. We shall also learn various types of functional groups present in ' organic compounds and classify these compounds into various classes on the basis of the functional groups. Finally, we will study, how to name the compounds &longing t o various classes.
.Objectives
After studying this unit, you should be able to : describe general features of a covalent b ~ n d , define bond length, bond angle and bond energy, explain various types of hybridisation of carbon compounds, identify the functional groups present in a molecule, give IUPAC names of various compounds belonghg to different classes, and write the correct structure of a compound from its name.
1.2 THE COVALENT BOND
The sharing of eltctrcrls to form a covalent bond leads to an increase in electron
dndslncnta~Concepts (^) density in between the nuclei. In such an arrangement, the forces holding the atoms together are also electrostatic in nature; but this time the forces operate between the electrons of one atom and the nucleus of the other. Such a system has
lower energy and is more stable as compared to the energy of isolated atoms. It is
so because each electron is now attracted by two nuclei. As a result, the formation of the bond is accompanied by the releascof the energy. The same amount of energy has to be supplied to break that particular bohd. The amdunt of energy required to break a particular bond (expressed in terrhs of kJ mol? is called its bond dissociation energy. You should not confuse bond dissociation energy with another term bond energy which is an average value for a particular bond. The difference in these two energies can beillustrated by taking the exampb of methane, CH4. If the C-Hbonds are successively broken as shown balm, then the bond dissociation energy for each step is as indicated on the right hand side. Bond Dissociation Energy
You can see from these values that the dissociation energies are different for each C-H bond breakage. On the other hand, bond energy is a single average value which &I be obtained as, 427+460+435+ Bond energy of the C-H bond = kJ mol-l 4
- -^1661 kJ mol-I = 415.25 kJ mol-I 4
Thus, the C-H bond energy in methane is one-fourth of the energy required for
the following change. CH4 .c. + 4 H.
Clearly, if the molecule is diatomic, then bond dissociation energy and bond energy are the same. Generally, bond dissociation energy values are more useful. Table'l. I lists the bond energies and bond dissociation energies for some bonds in
kJ mol-I (at 298 K and 1 atm. pressure). -
Bond Bond Bond Bond Bond Bond Dis- Bond Bond Dis- Energy Energy sociation sociation Energy Energy
H-H 436 N-N 163 CH3-H 427 Ph-OH^431 F-F 158 N = N 409 CH3CH2-H 418 Ph-NH2^381 CI-Ct' 242 N I N 945 CH3CH2CH2-H 410 Ph-F^485 Br-Br 193 0 - H 463 (CH3),CH-H 395.5 Ph-CI 406 1-1 151 0-0 146 (CH,),C-H 381 Ph-Br 301 H-F 165 O = O 497 CH3-CH3 3^68 Ph-I^272 H-CI 426.8 C - 0 3347 CH3-F 45 1 H-Br 364 C = O 694.5 CH3-CI 349 ;. H-I 297.1 O = C = O 803.3 CH3-Br 293 C-H 414 C-N 284.5 N3-I 234
C-F 484 C = N 615.1 HO-k 498
C-CI, 338 C = N 866.1 CH30-H^427 C-Br 276 N-H 389.1 CH3-OH 383 C- l 238 N - 0 200.8 Ph-H 43 1 C-C 348 N = O 606.7 PhCH2-H 356 C - C 612 S-H 347.3 Ph-CH3 389 C s C 813 S-S^ 225.9^ PhO-H^356 S = O 497.
Fundamental Concepts (^) and for
H O H
The skeletal structures or line structures show only the carbon-carbon bonds.
I II I H - C - C - C - H as CH3COCH3. I I
acetone
Repeating units such as (- CH2-) in the structural formula can be enclosed in brackets and hence hexane '
H H H H H H I I I I I I H - C - C - C - C - C - C - H I I I I I I H H H H H H hexane can be written as CH3(CH2),CH3.
Condensed formulas for compounds having multiple bounds can be written as shown below: H2C= CH2 HC s CH ethylene acetylene
For simple compounds, it is easy to write the condensed formulas. But, when the molecules are complex, these formulas look rather awkward and can be further abbreviated. These representations, are called line or skeletal structures. Here, the hydrogens are not shown and each end and bends represent the carbon atoms as shown below for some cases: Compound CH3CH2CH2CH2CH pentane
cyclohexane
1,ine structure
benzene
Having understood the above representations, answer the following SAQ.
SAQ 1 Write the condcrisrd i'orrnulas for thc following compounds:
Bonding, Functional Group Classification and Nomenclature
H - C - H H - C - H
I I
H - C - C - C - C - C - C - C - H
I l l 1 I I
H H H H
H-C-H
I
H
1.4 ORBITAL HYBRIDISATION
Properties and chemical reactions of most organic molecules can be easily
explained by considering the molecules to be formed by sharing of electron pairs
between the atoms. Another approach to formation of molecules which you
studied in Unit 5 of Block 1 in Atoms and Molecules course, is the molecular
orbital method. Organic chemists have for many years employed a bonding model
that combines elements of molecular orbital theory with Lewis model of formation
of covalent bond by electron sharing. This model was proposed by Pauling in 1930
and is based on the concept of orbital hybridisation. This model uses the
terminology of molecular orbital theory but treats the bonds between the atoms as
though they are localised, as in the case of diatomic molecules. In other words, it
is a sort of locahsed molecular orbital'treatment of the bond.
You have alreedv snidied in Unit 4, Block 1 of Atoms and Molecules course that
various types of orbital hybridisation is possible depending upon the number and
nature of the orbitals involved. Ih this unit, we will restrict our discussion to the
hybridisation involving s and p orbitals. Let us now study each type of
hybridisation involving s and p orbitals, in detail, to understand this concept and
its use in explaining the formation of molecules.
Let us consider the simplest organic compound, methane, having the molecular
formula CH4. You can recall that carbon has the electron configuration
ls2 2s2 2 p: 2p,!. Since only two unpaired electrons are there, one ;nay expect that
it should form only two bonds with two hydrogens to forms CH2. But actually it
forms four bonds with four hydrogens to give CH4. Pauling proposed that this
could be explained by using orbital hybridisation. In this method, atomic orbitals
are miied to yield the new hybrid orbitals. In this case, in the first step one of the
2s electrons is promoted to the 2pz orbital, electron configuration can then be
written as 2s' 2 p: 2p,! 2 p:. Bond formation with these pure atomic orbitals would
lead to the situation where the bond formed by one 2s electron will be different
from the bonds formed by three 2p electrons. But, in methane molecule, all the
four bonds are equivalent. In order to explain this, the idea of orbital
Hybridisation is a theoretical concept which enables as realistic modelling of molecular structure as possible.
The orbitah which undergo hybridisation, should not be energetically much different.
The number of hybrid orbitals generated is always equal to the number of atomic orbitals combined.
sp3 is pronounced as s-p-three and not s p cube.
The hybrid orbitals are obtained by mathematical combinations of atomic orbitals. 13
I
sp3 hybrid orbital has two lobes of unequal size separated from each other by a (^) Bonding. Functional Cretcp node. This situation is similar to a p orbital but with the difference that here one ( br\ification and Nnwlre(g(we lobe is very small and the other is very large. In other words, in sp3 hybrid orbitals, the electron density is concentrated in one direction which leads to greater (^) Remember that hybrid,sation overlap as compayd to pure atomic orbitals. Hence, the bonds formed by such (^) ~nvolves&ing of orb~talsof the orbitals will be stronger and more stable in comparison to those formed'by using (^) one and the same atom and not pure atomic orbitals. The spatial orientation of these orbitals is obtained by the^ orb~talso f^ d~fferentatoms. mathematical calculations and is shown in Fig. l.l(b). This is in accordance with the VSEPR theory which you studied in Unit 3, Block 1 of Atoms and Molecules course. You can see in the figure that these orbitals are directed towards the corners of a tetrahedron and the bond angle between any two sp3 hybrid orbitals is 109.5". In methane~molecule,each of the four sp3 hybrid orbitals overlaps with Is orbital of four hydrogens as shown in Fig. l.l(c). Note that the bonds so formed, i.e., the C - H bonds, are a (sigma) bonds. If instead of combining with hydrogens, the hybrid orbital forms a bond with the
similar hybrid orbital of another carbon atom, then a C - C bond will result
instead of the C - H bond. The C - C bond has a bond length of 154 pm and a
bond energy of 348 kJ mol-'. You will study more about the compounds involving sp3 hybridisation in Unit 6 of Block 2 of this course.
1.4.2 sp2-Hybridisation
In a molecule like ethylene, where there are not enough hydrogens in the molecule
to form six C - H bonds, another type of hybridisation has to be thought of.
In this type of hybridisation, as the name indicates, the 2s orbital of the carbon is hybridised with only two of the three available 2p orbitals, as shown below. 2p-Ft - mlx 2s and
[ N O 2p orb~tals o,.t,,t,ls -H 2+ Z W
2 p + + + I
alomlc carbon 1 5 + ls 22 ,' 2 p 2 Since three orbitals are hybridised, three equivalent sp2 hybrid orbitals are obtained. We shall now exp1a:n sp2 hybridisation using ethylene as an example. According to the VSEPR theory, these orbitals are oriemed in space making an angle of 120" with each other as shown in Fig. 1.2(a). Note thdt the three sp hybrid orbitals are in one plane. The third p orbital which is not utilised for hybridisation is perpendicular to the spZ hybrid orbitals and is shown in red colour in Fig. 1.2(a). When two such sp2 hybridised carbon atoms form a bond, the C - C bond formed is again a a bond. I f the rest of the sp2 hybrid orbitals on each carbon atom overlap with 1s orbital of the two hydrogen atoms, then as shown in Fig. 1.2(b), the two unhybridised p orbitals on the two carbon atoms are parallel to each other. These p orbitals can overlap sideways to yield a second bond, known as a
(pi) bond which is shown in Fig. 1.2(c). The C = C bond length for ethylene
molecule so obtained is 134 pm. You can compare this value with C - C single
bond length as given before in case of ethane. You will study in detail, the compounds having sp2 hybridised carbon atoms such as alkenes 3nd dienes in carbon in e~hylene
,Fundrmenlal Concepts
sp2 orbitals
You are aware that: i)a bonds are formed by the edge-on overlap of pure (s and p ) or hybrid orbitals. The electron density in a bonds is maximum along the internuclear axis. ii) T bonds are formed by sideways overlap of p orbitals. r bonds have maximum electron density above and below t h e internuclear axis.
Activity Wake a model of ethylene molecule and convince yourself that it is flat in shape with the two carbons and their substituent hydrogens lying in one plane. However, the r bond is a t right angles to this plane.
I
sp2 hybrid orbitals of carbon form o bonds witheach other and hydrogens
overlap lo form rr
bond H ...
C-C o bond
Fig. 1.2 : a) s p 2 hybrid orbitals. b) Formation of C - C a bond. c) Formation of a r bond in ethylene molecule.
.SAQ 2 Predict the percentage of s and p characjer in sp2 hybrid orbitals.
Let us now consider the third type o f hybridisation involving s and p orbitals in
cases where a triple bond is'stipulated. In carbon atom when 2s and only one of
the three 2p orbitals hybridise as shown below, the hybridisation is known as sp-
i
mix 2s and b two, hyhrid .+ one 2p orbital orh,la
carbon in acctylcnc
Fundamental Concepts (^) SAQ 3
Indicate the type of hybridisation for each of the carbon atoms in the following compounds:
1.5 FUNCTIONAL GROUP CLASSIFICATION
A systematic study of chemistry or for that matter any other branch of science, is not possible without arranging the subject matter in a logical manner when sufficient data has accumulated. In case of inorganic chemistry, formulation of the periodic table stimulated not only the search for missing elements but also led to the understanding of the periodic behaviour. In organic chemistry, as the number of known organic compounds runs into millions, it is very difficult to study each and every compound individually. Thus, by grouping similar compounds together in a class or a family, it is easier to understand their properties, reactions etc. One way of such classification is based on the functional groups. A functional group can be defined as an atom or a group of atoms in a molecule which exhibits characteristic chemical properties. Such chemical properties exhibited by the functional group are more or less constant for various compounds having different carbon chains. Indeed, many organic reactions involve transformation of the functional group and do not affect the rest of the molecule. The advantage of such a classification based on functional groups is that in addition to logically systematising the organic compounds, the properties of thc compounds can be predicted just by looking at their structures, i.e., by knowing the type of functional group present. Table 1.4 lists a number of important functional groups. (^) I You will study each class of compounds in detail in the forthcoming blocks of this i course. Table 1.4 : Functional Groups
Class Functional General structural Example IUPAC suffix or Group formula prefix Containing C ond H only Alkane none R - H CH4 -ane methane
R \ / \ / R Alkene /C = c (^) \ /C = C (^) \ H2Cethylene =CHI -ene Rl R Alkyne - C = C - R - C m C - R , H - C m C - H acetylene
-Yne I
cyclohexace (n = 4)
Aromatic Compounds
I
Bondiy, Functbnni Group Uassifkstion nnd IYORli)ndnturc
benzene Containing C,H and 0 Alcohol -OH R-OH CH, -OH - methanol
Ketone -
0 0 II II
R - C - R ' CH, - C - CH, -one
acetone
I
methyl acetate I 0 0 0 0 I 0 0 II I 1 I I II II II
I
Anhydride - C - 0 - C - R - C - 0 - C - R ' CH3-C-0-C-CH3-oic ~ 1 acetic anhydride anhydri~fc 1 i
Nitrile - C = N
Containing C, H, N a n d 0 Nitro - NO, compou~~ds
.. (primary amine) R' I
R'
I I
R - N- R" H3C - N- CH
(tertiary amine) trimethylamine'"' J
N-R" N - CH
methylamine R--C-N CH,-C=N - nitrile acetonitrile
R - NO2 CH, - NO2 Nitro - niLrorr?ethane
C - N ' R-C-NH, CH3-C - NH: - arnide \ (^) aceramide
two or three. The carbon-nitrogen double bond is characteristic of the class of Bonding, Functional Group compounds known as imines while compounds having carbon-nitrogen triple bond C'aSSifica"On^ and^ Nomenc'a'ure are called nitriles. Then we have alkyl halides which have their unique importance in the transformation of functional groups which you'will realise when you study (^) The terms primorg, secondary their reactions in the following blocks. The sulphur analogs of alcohols and (^) and terttary as used for carboxylic acids are known as thiols and sulphonic acids, respectively. (^) classification of branched alkyl
Parallel to the classes discussed above for aliphatic compounds, we have aroniatic ~ ~ ~ ~ ~ ~ o ~ f n : ; ~ ~ ~ compounds in which benzene forms the backbone to which various functional (^) branched chain alkanes in the groups mentioned abo.ve can be attached t o yield similar classes of aromatic (^) next section compainds, like aryl halides, arylamines, phenols,, aromatic carbonyl compounds, aromatic acids and their derivatives, etc. As you have seen in Table 1.4, R is generany used to represent an alkyl group; the corresponding aromatic compounds
are obtained by replacing R by Ar which denotes an aryl group; this is shown in
Table 1.4 in case of alcohol and phenol. In the next section, we will study about the nomenclature of these compounds. Before that attempt the following SAQ to check your understanding about the functional groups.
SAQ 4
Encircle and name the functional groups present in 'the following compounds:
a) CH3- CH = CH - CH20H
..........................................................................................................
b) CH3COCH2CH2-^0 -^ CH
I I
..........................................................................................................
CH
I
c) (= 3 CH 2 - N-CH 3
..........................................................................................................
I I I 1 d) QHCCH2CH-^ C^ -^^0 -^ C^ -^ CH2CH I
CH
......................................................................................................*...
1.6 NOMENCLATURE OF ORGANIC COMPOUNDS
Isomers are the compounds that have identical molecular formulas but differ in the ways in which the atoms are bonded to each The earliest attempts to name organic compounds were based either on their origin other.^ For^ example,^ four^ carbons or on their properties. For example, citric acid was named so because of its In^ a hydrocarbon having
occucrence in citrus fruits. The aromatic compounds were called so because of molecular formula^ C4H10can be
arranged in the two different
their characteristic odour (Greek: aroma, fragrant smell). Examples are oil of ways:
wintergreen and vanillin (a constituent of vanilla also used as a flabouring agent) (^) Straight which were called aromatic due to their characteristic fragrance. With the (^) HyC - CH2 - CH2 - CH, advancement and growth in the knowledge of chemistry, the number of known (^) common name : normal butane organic compounds has increased rapidly. Also, with the increase in the number of or^ n-butane carbon atoms, the number of possible isomers for hydrocarbons (without any Branched^ cham functional group) becomes very large (see Table 1.5). CHY I H3C - CH - CH, Table 1.5 : Possible Number of Isomers for Hydrocarbons (^) common name : isobutane
Number o f carbon Ibus. are iramn.^ n-butme^ md^ isc&hne atoms in the hydrocarbon 4 5 6 7 8 9 1 0 1 2 1 5 2 0 Number of possible isomers 2 3 5 9 18 35 75 355 4,:17 366,
Fundamental Concepts (^) Having learnt about the variety of functional groups, you can imagine that the nature and position of functional groups present can raise these numbers many fold. Under such a situation, it is next to impossible to learn the names randomly assigned to the compounds, especially when there is no correlation of the name to the structure of the compound. This necessitated the need to have a systematic nomenclature for which the International Committee of Chemists met at Geneva in
- The work was carried on by the International Union of Chemists (I.U.C.) which gave its report in 1931, known as the I.U.C. system of nomenclature. As the nomenclature is always undergoing modifications and revisions, the latest rules which are widely accepted were recommended by the Commission on Nomenclature of Organic Chemistry of the International Uniod of Pure and Applied Chemistry (I.U.P.A.C.). We will now study this system in detail.
Since the nomenclature of other classes of compounds is based on the nomenclature of alkanes, let us start the study of nomenclature with the alkanes.
Alkanes are represented by the general formula CnH2n+2 where n can be
1, 2, 3, J... etc. The first four alkanes retain their original or nonsystematic names The names of alkanes higher than these start with a prefix (Greek or Latin words) which indicates the number of carbon atoms in the chain and end with suffix-ane. The IUPAC names for various alkanes having different chain lengths are given in Table 1.6. The unbranched alkanes have their common names as normal alkanes
Compounds that differ from each other in their molecular formulas by the unit - CH, - are called members of a homolagorr serks. Thus. the compounds listed in Table 1. belong to a homologous series.
Tohle 1.6 : IUPAC Names of straight chain alkanes having general formula CnHZn+
n Formula
1 CH,
Name
methane ethane propane butane pentane hexane heptane octane nonane decane
n Formula Name
undecane dodecane tridecane tetradecane pentadecane I. icosane triacontane tetracontane pentacontane hectane
'Prior to 1979 version of IUPAC rules. it was spelled as eicosane.
Fundnmenlnl Concepls
Note that here ethyl is cited before methyl, in spite of its higher location number.
Similarly, the con~poundshown below,
H3C CH
can be named as 4isopropfi-5.5-dimdhylnonane or C(1-methylethyl)-5,
5-dimethylnonane.
7. The branched chain substituents, such as 1-methylethyl shown in step 6, are
numbered starting from the carbon attached directly to the parent chain. Table
1.7 shows the numbering for the branched substituents listed there. The longest
carbon chain is selected and the substituents are named according to the rules
listed above for compounds having unbranched substituenfs. Note that the
name and numbering of branched substituent is written in brackets in order to
separate it from the numbering of the main chain.
8. The alkyl substituents can be further classified as primary, secondary or
tertiary. An alkyl group is called a primary alkyl group if the carbon atom at
the point of attachment is bonded to only one other carb6n. For example,
R - CH, - is a primary alkyl group. Similarly, a secondary alkyl group has
two alkyl groups bonded to the carbon atom taken as the point of attachment
to the main chain. Thus, .a secondary alkyl group can be written as shown
below:
R I
R - C -
A\ point of attachment
secondary alkyl group
Similarly, a tertiary alkyl group has three carbon atoms bonded to the carbon
atom taken as point of attachment. Thus, a tertiary alkyl group can be
represented as shown below:
R
I
R - C -
1 \point of attachment
R
tertiary alkyl group
9. When more than one carbon chains of equal length are available, the
numbering is done considering the following points:
(a) The principal chain should have the greatest number of side chains. For
example, in the compound shown below, ,
1 3 4 5 6 1 8
1 C H 3 - b - C H - C H 2 - C H - H - C H ~ - C &
1 6 5 C f ; z 1
CH3 CHI CH3 CH
17
CH
8
I the chain having numbering in red colour has^ four^ side chains while the^ ~eadhg,Fu.eti6.aI^ ~lou,
chain marked with numbers in black colour hiis three'side chains. So the cIasri(k.tioll^ MANoameWm
principal chain is the one which is marked in the red colour. Hence, the
name is 3-ethyl-2,5,6-trimethyloctane.
(b) The chain having the lowest number for substituents is chosen as the
principal chaiu. In the compound shown below,
if the numbering is done as shown in black colour, the name would have
substituents at positions 3, 4 and 5. But, if the carbon chain numbered' in
red colour is taken as the principal chain, then the substituents get the numbers 2, 3 and 4, which is obviously the correct choice.
Till now we were studying the nomenclature of alkanes.'Let us now study how various cornbounds having different functional groups are named. In case of
compounds which have a functional group, the functional group gets a precedence
over the alkyl substituents. At this stage, you refer back to Table 1.4 where IUPAC prefixes and suffixes for various classes of compounds are given.
Akenes: The suffur ane of the parent hydrocarbon is changed to ene and the
functional group (a double bond in this case) is given the lowest possible number. Some examples are: CH2= CH2 CH3CH^ =^ CHI ethene propene 1 (~ornrnon$arne^ :^ ethylene)
Alkynes: In this case suffix ane of the parent hydrocarbon is changed to yne. As
expected, here also the functional group is given the lowest number.
I^ CH HC E CH
I C H 3 - C H - C s C - C H 3 ethyne 5 4 3 ' 2 1
When both double and triple bonds are present, then the double bond gets the lower number. Thus, for the compound shown below,
(^1) the correct name is pent-1-ene-4-yne.
Alkyl halides: The alkyl halides are the w e n derivatives-of alkanes. The -
(
halogens present are usually F, CI. Br and T.-The commolntunes are arrived at by
writing the name of alkyl group followed-by the name of the halide. Examples are
shown below :
CH
I
CH3CH2CH2CH2Cl CH3- CH - CH2Br
n-butyl chloride isobutyl bromide
In the IUPAC system of nomenclature, prefm halo- (i.e., fluoro-, chloro-, bromo-
or iodo-) is used and the carbon chain is so numbered to give the lowest number
CH
4 3 ) 2 I CH3 - C - CH2- CHO
I
CH
is named as 3, 3-dimethylb~anal.
Ketones: The common names for ketones are written similar to ethers, i.e. the two
alkyl groups are written alphabetically followed by the word ketone. For example,
the compound,
is commonly known as ethyl methyl ketone.
II
Thus, acetone, CH3CCH3is also known as dimethyl ketone. The IUPAC names
for ketones are derived by using the suffix one instead of final e of the parent
hydrocarbon. As usual, the position of the carbonyl group is indicated by the
lowest possible number. A few examples are,
I I I I CH3- C - CH3 CH3-CH2-CH2-C-CH propanone 5 4 3 2 1
Carboxylic acids: Nowhere else in organic chemistry, the common names are so
prevalent as they are among carboxylic acids. Some examples are listed in Table
1.8 along with both their common and IUPAC names. For monocarboxylic acids.
[i.e. acids having one carboxy (- c -OH) group], the IUPAC names are derived
Table 1.8 : Some Carboxylic Acids
CH3(CH316COOH
H02C - C02H
H02C(CH2)4C02H
0 I 1 CH2 = CHCOH
OH
HOOC - CH - CH -COOH
Common Name 1 IUPAC Name I
Formic acid
Acetic acid
Lactic acid
Stearic acid Oxalic acid Adipic acid
Acrylic acid
Tartaric acid
methanoic acid
ethanoic acid
2-hydroxypropanoic acid ' octadecanoic acid ethanedioic acid hexanedioic acid
propenoic acid
2,3-dihydroxybutanedioic acid
Bonding, Functional Group Classification and Nomenclature
k'undamcnlnl Concepls by replacing e ending of the alkane by oic acid. As for aldehydes, the carboxyl
carbon is numbered 1. However, in case of the dicarboxylic acids, the final e of the hydrocarbon is not dropped. Acyl halides: Acyl halides are commonly named by placing the names of the halide after the name of the acyl group. The acyl group is obtained from the carboxylic 0 I I
I I
acid by removal of its hydroxyl portion, i.e. R - C - O H leads to R - C - acyl
group. The acyl group is named by using yl i s the ending instead of ending ic in
the carboxylic acid. Some such examples are:
I I
C H t C - C
I I C H 3 - C H 2 - C - I (.a$$'+ yl -, .cclyl) .atyl chloride
propanoyl iodide
IUPAC names for acyl groups use the ending oyl instead of ending e in the name
of the corresponding hydrocarbon. The aceQl chloride has the IUPAC name 0
ethanovl chloride. Another e x a m ~ l eis
CH3\ I
CHC - C1 which is named as
2-methylpropanoyl chloride. / 2 I .CH3 J Acid amides: The common names for acid amides are derived by replacing the
suffix ic or oic of the carboxylic acid by the suffix amide as shown below:
C H ~ C- NH
(acetic - acetamide)
The IUPAC name for an amide is derived by appending the suffix amide to the
parent hydrocarbon with the final e dropped. Thus, acetamide has the IUPAC
name ethanamide. Having done this, can you give common and 1UPAC names for
I I
HC - NH,? These are forrnarnide and methanamide, respectively.
Acid anhydrides: A symmetrical anhydride is named as anhydride of the parent 0 I I R.
acid. Thus, CH3- C - 0 - C - CH3, the anhydride which is obtained from ethanoic
acid (common name: acetic acid) is commonly known is acetic anhydride. The IUPAC name for this anhydride is ethanoic anhydride.
For mixed anhydrides, both the parent carboxylic acids are cited in alphabetical order, followed by the word anhydride, as illustrated below:
ethanoic methanoic anhydride (common name : acetic formic anhydride) Esters: As the esters contain alkyl and alkanoyl (acyl) groups, they are named as alkyl alkanoates. The alkyl group is cited first,, followed by the name of the alkanoyl (acyl) portion which is named by replacing the ic ending of the carboxylic
acid by the suffix ate.
methyl ethanoate ethyl ethanoate methyl^ propanoate
Amines: There are two systems of naming amines. One method names them as alkylamines and the other calls them as alkanamines. The alkanamine naming system was introduced by Chemical Abstracts and is easier to use as compared to 28 the earlier IUPAC system of^ aikylamine^ names. The latest revision of IUPAC rules accepts both systems and examples below are named in both the ways.
