organic nomenclature

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Nomenclature of organic compounds - Part I
Stanislaw Skonieczny and Andrew P. Dicks <sskoniec@chem.utoronto.ca, adicks@chem.utoronto.ca>
Department of Chemist')'. University o(Toronto
Toronto ON M5S 3H6
Butane
Heptane
Propane
Hexane
Ethane
Pentane
Methane
Systematic names of all other members of the series are formed
by combining the ending "-ane" with the Greek (sometimes also
the Latin) numerals indicating the number of carbon atoms in the
chain.
The first four members of the series have semi-trivial names4
(i) Alkanes (CnH2n+2l
Nomenclature of specific compound types
2. Determine the parent hydrocarbon (principal chain or parent
ring system containing the principal functional group).
3. Name the parent hydrocarbon and the principal group(s).
Give the parent the same name as if it were an alkane, but
replace "_e"with the suffix characteristic of the highest
priority functional group.
4. Number the parent hydrocarbon such that the highest priority
group has the smaller number.
5. Name alkyl groups, halides and other substituents. Determine
their position on the parent hydrocarbon by numbering
established in Rule 4.
6. Assign stereochemistry where appropriate to chiral carbon
atom(s) (stereocentres) and double bond(s).
7. Write the complete compound name as a single word with
correct locants for all substituents, which are listed in
alphabetical order. In alphabetizing, ignore prefixes such as
sec-, tert-, di, tri, etc., but include iso- and cyclo-.Functional Group - an atom or group of atoms (e.g., a hydroxyl
group (-OH)) that replaces hydrogen in an organic compound,
defining the structure of a family of compounds and determining
properties of the family.
Locant - letter or numeral indicating the position of a
substituent.
Parent Hydrocarbon - most important molecular skeleton
designated according to IUPAC priority rules.
Prefix - a substituent name listed before the parent
hydrocarbon.
Principal Functional Group - highest priority functional group.
Substituent - functional group or atom that substitutes a
hydrogen atom in the parent hydrocarbon.
Substitutive Name - name indicating substitution of H atom(s) in
the parent hydrocarbon.
Suffix - name of the principal functional group listed after the
name of the parent hydrocarbon.
Trivial Name - name without components of systematic
meaning.
Abbreviations and terminology Used2
Introduction
Naming organic compounds is an important component of the
Canadian high school chemistry curriculum.' However, high
school textbooks are often inconsistent and dated in their
application of International Union of Pure and Applied Chemistry
(IUPAC) nomenclature rules. As more and more post-secondary
institutions teach organic chemistry in first-year courses, the
importance of using appropriate nomenclature is clearly apparent.
This article is written to briefly summarize fundamentals of
systematic organic nomenclature with appropriate examples and
deals with naming of aliphatic hydrocarbons, haloalkanes and
aromatic compounds. Part II will cover nomenclature of alcohols,
ethers, ketones, aldehydes, carboxylic acids, esters, amides,
and amines.
General guidelines for naming organic compounds
Straight chain alkyl groups are formed by removal of a hydrogen
atom from the terminal -CH3 group of the corresponding alkane.
The name is formed by replacing the "-ane" ending by"-yl".
The "-y1"position is given the locant "1" in numbering the chains.
Construction of the systematic name for an organic compound
involves several steps, to be taken as far as applicable in the
following order:
1. Determine the principal functional group in the compound.
When more than one functionality is present, the principal
group is that which has highest precedence (see Table 1 in
Part II). This group is cited as the suffix; all other groups are
cited as prefixes.3
-CH3
Methyl Ethyl
-CH~CH2CH3 -CH2CH2CH2CH3
Propyl Butyl
October 2009/Chem 13 News 9
Nomenclature of Unsaturated Hydrocarbons
3 42
But-2-ynePentc1-ene
In naming unsaturated chains, the "-ane" ending of the
corresponding saturated chain is changed to "-ene" (for one double
bond) or to "-yne" (for one triple bond). In order to indicate the
position of a multiple bond, number carbon atoms in the chain
giving lowest possible numbers to carbon atoms in the multiple
bond. Only the lower of the two locants for the carbon atoms of
an unsaturated bond is cited.
2 4
1~5
lett-Butyl
1,1-0imethylethyl
Branched Alkyl Groups
Systematic names are formed by indicating positions and names
of substituents. Some simple and unsubstituted branched alkyl
groups may also be named by their trivial names (so-called
retained trivial names).6
-CH(CH3l2 -CH2CH(CH3l2 -CH(CH3)CH2CH3
lUPAC: 1-Methylethyl 2-Methylpropyl 1-Methylpropyl
Retained
trivial Isopropyl Isobutyl sec-Butyl
name:
(ii) Cycloalkanes (CnH2n)
Note that italics are never capitalized and are omitted while
alphabetizing substituents.
Cycloalkanes are named by applying the prefix "cyclo" to the
name of the alkane with the same number of carbon atoms.
The prefix "cyclo" is a part of the name (capitalized and used to
alphabetize ).
654 3
1
rG5
3 4
1. Carbon-carbon double and triple bonds constitute functional
groups.
2. The parent hydrocarbon is that which contains the maximum
number of multiple bonds. If more than one such chain is
found, the longest is chosen as the parent. Both carbon
atoms of multiple bonds must be included in the parent
hydrocarbon.
3. Unsaturation is always indicated in the suffix of the name. If
a higher priority group is present, the" -en-" and "-yn-"
suffixes are used.7
4. Number the chain (or ring) of carbons such that the carbon
atoms of multiple bonds have the lower position number,
since the multiple bond has a higher priority than any alkyl
or halide substituent.
5. Name substituents and assign their locants.
6. Assign stereochemistry to di-, trio, and tetra-substituted
alkenes.8
7. Use the suffixes "-adiene", "-adiyne", "-atriene",
"-atetraene", etc., for compounds with multiple double and
triple bonds. ..
o
Cyclohexane
o
Cyclopentane
D
CyclobutaneCyclopropane
Simple alkanes and cycloalkanes do not possess functional
groups, so Step 1 is omitted from their nomenclature. When
there are two or more longest chains of equal length, the chain
with the greater number of substituents is the parent. Number
the chain or the ring in the direction such that the position of the
first substituent has the smaller number. If the first substituent
.from either end has the same number, number from the end
nearer a second substituent (and so on). The name of a
branched hydrocarbon is composed of the parent chain name
and substituent prefixes.
7
~
6
1 3'
2 4 5
4-Ethyl-2-methylheptane
2
~
4 5
1-Ethyl-3-methylcyclopentane
(l)-2-Ethylpenta-1,3-diene
2
) .;
)5
7 6
2-Methylhex-1-en-4-yne
1Jl36U4
5
(iii) Alkenes (CnH2n) and Alkynes ,(CnH2N-2) (3E,5E)-5-Methylhepta-3,5-dien-1-yne 2-Methylcyclohexa-1,3-diene
Some common unsaturated hydrocarbons have retained trivial
names6:
(iv) Haloalkanes (formerly known as alkyl halides)
BryZr2U4
1 5
H2C=CH2 ~ HC=CH
IUPAC: Ethene 2-Methylbuta-1,3-diene Ethyne
Retained
Ethylenetrivial Isoprene Acetylene
name:
Halogens (together with alkyl groups and a nitro group) are
always named as substituents and listed as prefixes.9
6
M1 3 CI
10 Chern 13 News/October 2009
3,3-Dibromocyclopentene (E)-4-Chloro-2-methylhex -3-ene
(v) Aromatic Coml}()unch. (il/r.llll/'.) {i Trivial and Semisystematic Names Retained for Naming Organic
Compounds www.acdlabs.comliupaclnomenclaturel93!r93_671.htm
(accessed January 2009).
7. RB. Fox, W.H. Powell. Nomenclature of Organic Compounds.
Principlesand Practice, 2nd edition, Oxford University Press, Oxford
2001.
8. S. Skonieczny. A.P. Dicks, Chem 13 News, January 2009.
9. D. Hellwinkel, Systematic Nomenclature of Organic Chemistry, A
Directory to Comprehension and Application of its Basic Principles,
Springer, Ber1in, New YorK, London 2001.
10. J. Rigaudy, S.P. Klesney. Nomenclalure of Organic Chemistry,
Sections A, B, C. D. E. F, and H, 1979 edition, Pergamon Press.
Oxford 1979. •
p-Dibromobenzene
1.4-Dibromobenzene
Br-C>-Br
1-Bromo-2-chloro-5-fluor0-4-methylbenzene
m-Chlorololuene
1-Chloro-3-methylbenzene
r'
l
2-Ethyl-1,4-dimethylbenzene
/~l 2)
0/
6l;/IJ ~I
IUPAC M"lhyll","Il"'" 1 M"lhvlulhylbunzene Methoxybenzene
Retained
trivial name 'Tolt""I" Clunrmo Anisole
When three or more substiluents are present, only numbers can
be used. The lowest possible numbers are assigned.
6
li1BrSI4 #2 CI
3
When more than ono substituont is present. their positions are
usually indicated by numbers. However, 0- (orlho), Tn- (meta)
and p- (para) may be used in place of 1.2-, 1,3-, and 1,4-,
respectively, when only two substituents are present.
&
HiUh Sd101Illoxlbo'llill 1I111il lllroCtlr.'1lll/l 0
'
1110111,1"': CllfllPlJlJlllls 10
henzene aml.ll' (1""\1rtliv"'~1 :;"';lllnikyl UlOllp". ""\iiIIlS. nitro
groups. and alkoxv (1'0111':\;1"1 llIUillllwl 'Ib ~ub~tltll/lnts am'
used LIS profrXII!. I llt 1ll0/lllt'I,IUII't'lllld flllll1l11lic compounds. the
point of allar""I1'1lf of III" ltlll>:l1IIII,,"1 ht)(;olmm •.mhon 1 Clndis
traditionally Ollllll"d !~l""flIIlvllllllilllllll' or lTlonosubstituted
aromatic COIllIHJlIIlIlr. ,'"1 1Illllllll1d Ily IUI'I\C Itl
1.2.Dlmt'lhylbenzene
IUPAC
accepted ()- Xylem,
References Nick Kim, www.//lab-initio.com/
1. Pan-Canadian Protocol Grade 11-12 Chemistry Specific Leaming
Outcomes. Council of Ministers of Education. Canada
2. U BOnzli-Trepp. Systematic Nomenclature of Organic,
Organometallic and Coordination Chemistry, CRC Press, Lausanne
2007.
3. S Skonieczny. Joumal of Chemical Education. 2006, 83. 1633-1637.
4. G.J Leigh. H.A. Favre. W.v. Metanomski. Principles of Chemical
Nomenclature, A Guide to IUPAC Recommendations: Blackwell
Science. Oxford 1998
5 R. Panico. W.H. Powell. J.-C Richer. A Guide to IUPAC Nomenclature
of Organic Compounds, Recommendations 1993. Blackwell Science.
Oxford 1993.
Nomenclature of organic compounds - Part II
Stanislaw Skonieczny and Andrew P. Dicks <sskoniec@chem.utoronto.ca, adicks@chem.utoronto.ca>
Department o/Chemistry, University o/Toronto, Toronto ON M5S 3H6
Introduction Substituents are always listed as prefixes:
The suffixes "-diol", "-triol", "-tetrao!", etc. are used for multiple-
OH groups. Contrary to nomenclature of alcohols, the terminal
"-e" is retained in the name of parent hydrocarbon.
HO~ HO~OH H0-o-0HOH
Ethane-1,2-diol Propane-1,3-diol Benzene-1,4-diol
Phenols
HO~ ).
5
( j-OH n~ I.CI 3 1 OH
6 5 2
Phenol 2-Methylphenol 3-Chlorophenol
(ii) Ethers
Examples when a multiple bond is present:
~4\JOH
3 2
n341 IiHO 6 Br
5-Bromo-2-methylcydohexan-1-o1
Prop-2-yn-1-o1 6-Methylcyclohex-2-en-1-o1
Propargyl alcohol
CI OH
CI~1
3
4.4-Dichlorobutan-2-ol
2
HO~
3
HO~
3
2-Methylpropan-1-o1
IUPAC: Prop-2-en-l-01
Retained
trivial name: Allyl alcohol
Dials
Alcohol - a compound in which a hydroxyl functional group
(-OH), is attached to a saturated (sp3 hybridized) carbon atom.
Aryl Group - a group formed by a removal of a hydrogen atom
from an aromatic ring carbon atom, abbreviated as Ar.
Functional Group - an atom or group of atoms (e.g., a hydroxyl
group (-OH)) that replaces hydrogen in an organic compound,
defining the structure of a family of compounds and determining
properties of the family.
Parent Hydrocarbon - most important molecular skeleton
designated according to IUPAC priority rules.
Phenol - a compound in which one or more hydroxyl groups
is/are attached to an aromatic ring.
Phenyl Group - CsHs-, abbreviated as Ph.
Prefix - a substituent name listed before the parent
hydrocarbon.
Principal Functional Group - highest priority functional group
(see Table 1).
R - abbreviation used to represent an alkyl group.
Suffix - name of the principal functional group listed after the
name of the parent hydrocarbon.
(i) Alcohols
Abbreviations and terms used1
Nomenclature of specific functional groups
This paper is the second part of two articles that summarize the
fundamentals of systematic organic nomenclature. Part II covers
nomenclature of the following functional groups: alcohols,
ethers, ketones, aldehydes, carboxylic acids, esters, amides, and
amines. Part I was published in the October 2009 issue of Chern
13 News.
The presence of a hydroxyl group (-OH) as the principal
functional group is indicated by the suffix" -01" replacing the
terminal "-en in the parent hydrocarbon name. The longest
carbon chain is numbered so as to give the carbon bearing the
hydroxyl group the lowest possible number. This number is used
to denote the position of the hydroxyl and is placed just before
the suffix "-01". In the case of methanol and unsubstitlited
ethanol, the locants are omitted.2
Methanol
2
3~OH
Propan-1-o1
OH
3~1
Propan-2-o1
The shorter of the two chains becomes the first part of the name
with the "-ane" suffix changed to U-oxy", and the longer alkane
chain becomes the suffix of the ether name.
-OCH3 -OCH2CH2CH3 -OPh -OCH2Ph
Methoxy Propoxy Phenoxy Benzyloxy
1
K/0, "'-../0, 4 oJ
Methoxymethane Methoxyethane 2-Ethoxybutane
(not ethoxymethane)
November 2009/Chem 13 News 13
'-0 0-/° ~ II ~ II 0
IUPAC Methoxybenzene Ethoxybenzene
Retained
trh/iel name: Anisole Phenetole
Ethoxyethene
Ethyl vinyl ether
O~6
Y0fo
H
IUPAC: Benzenecarbaldehyde 3-0xocyclopentanecarbaldehyde
Shorter name
accepted by IUPAC: Benzaldehyde
(v) Carboxylic acids
(iii) Ketones
In general, ketones (R-CO-R) take the suffix "-one" with a fixed
position number.
y
~ }-Q0 1 3 6 7 2
IUPAC: Propan-2-(lne 2.6-0imethylhepta-2.5-dten-4-(lne l-Phenylethan-1-(lne
Retained
trivial name' Acetone Phorone Acetophenone
Carboxylic acid groups (-COOH) in acyclic hydrocarbons are
denoted by adding the suffix" -oic acid" with elision of the final "-
e" before "0".3 Since the carboxylic group is always at the end
and has highest priority, it takes position "1" and the locant is
omitted.4
H yOH
OH
HoAo
O~CI
0 2 3
IUPAC: Methanoic acid Ethanoic acid 3-Chloropropanoic acid
Retained
trivial name: Formic Acid Acetic acid 3-Chloropropionic acid
If a higher precedence suffix exists, the prefix "oxo-" is used:
O')!-OH
O~_
3
o
5~OH
o
IUPAC
Retained
trivial name:
(S)-2-Hydroxypropanoic acid
Lactic acid
#HHO 4 23 1 OH
o OH
2,3-0ihydroxybutanedioic acid
Tarlanc acid
IUPAC: 2-0xopropanoic acid 4-0xopentanoic acid
Retained
trivial name: Pyruvic acid Levulinic acid
(iv) Aldehydes
When a carboxylic acid group is attached to a carbocyclic ring,
the suffix" -carboxylic acid" is added to the name of the parent
hydrocarbon without removal of the final "_e".4The principal
group assumes position 1.
Esters (RCOOR') are named as alkyl derivatives of carboxylic
acids. The alkyl (R') group is named first. The RCOO-
component is then named as a separate word based on the
carboxylic acid name, with the ending changed from "-oic acid"
to "-oate".5
IUPAC: Methyl ethanoate
Retained
trivial name: Methyl acetate
Aldehydes are named using the suffixes "-a I" for -(C)HO
(when the aldehyde carbon is a part of the carbon chain). The
aldehyde carbon is always carbon 1, hence it is omitted in the
name.
H H 0Y'")=0 oAH H
IUPAC: Methanal Ethanal Propanal
Retained
trivial name: Formaldehyde Acetaldehyde PropionaldehydeThe suffix "-carbaldehyde': is used when the -CHO group is
attached to the carbon atom of a ring. The name of the parent
ring is retained in full.
14 Chem 13News/November 2009
IUPAC:
Retained
trivial name'
(vi) Esters
Benzenecarboxylic acid
Benzoic acid
HO~.
O~
Br
5-Bromo.2.hydroxycyclohexanecarboxylic acid
21~'
3
2-Methylpropyl propanoate
Isobutyl propionate
(vii) Amides Table 1. Decreasing Order of Precedence for the Major
Functional Groups6
Amines are named for the attached alkane chain with the suffix
"-amine" with fixed position number. 5
Amides take the suffix "-amide". No locant is required since an
amide group always terminates a carbon chain. Alkyl chains
bonded to the nitrogen atom in secondary and tertiary amides
are treated as substituents with the locant prefix "N_".5
Functional Suffix if Highest Prefix if Lower
Group Precedencea Precedence
-(C)OOHb -oic acid -
-eOOH -carboxylic acid carboxy-
-eOOR alkyl carboxylate alkoxycarbonyl-
-(C)ONH2b -amide -
-eONH2 -earboxamide carbamoyl-
-G=-N -nitrile cyano-
-(C)Hob -81 oxo-
-eHO -carbaldehyde formyl-
>c=O -one oxo-
-QH -01 hydroxy-
-NH2 -amine amino-
>C=C< -ene *
-C=C- -yne **
-X, -R, -OR, **"
halo-, alky/-,
-Ar. -N02 alkoxy-, aryl-, nitro-
3,N.Dimethylbenzene<:artlo.amlde
3.N-Dimethy1benzamide
N.IY-O,methy1methanamldeEthanamide
NHz
""""""'NHz HzN~ ~
IUPAC: Ethanamine Propan-1-amine Butan-2-amine
Retained
trivial name: Ethylamine Propylamine sec-Butylamine
Retained
trivial name: Acetamide N,N-Oimethytformamide
(viii) Amines
'N/'-......
H
For secondary and tertiary amines, the longest carbon chain
attached to the nitrogen atom becomes the primary name of the
amine; the other chains are prefixed as alkyl substituents.5
/
iN\......../
N-Methylethanamine N-Ethyl-N-methylpropan-1-amine
Editor's note
On the University of Water100 chemistry website, the following
advice is given to students for Chem 266. Basic Organic
Chemistry 1, often the first university organic course students see.
a Locants (numerals andlor letters) are placed immediately
before the part of the name to which they relate.
b (C) designates a carbon atom included in the name of the
parent hydrocarbon (it does not belong to a group
designated by a suffix or a prefix).
Always used as a suffix. However, if a higher priority group
is present in the molecule, the suffix is changed to "-en-"
and is followed by the suffix of the higher priority group.
Always used as a suffix. However, if a higher priority group
is present in the molecule. the suffix is changed to "-yn-"
and is followed by the suffix of the higher priority group.
*** Always used as a prefix.
If you do not learn the names of compounds you will not be able
to follow along in class. It's like your Dad asking you to get the
doohicky from behind the thingamajig that's in the garage. All
you know is that you have to go to the garage but you have no
idea what he is talking about. You don't want this to happen in
class. You may know that I am talking about an E2 reaction but
what the heck is a t-butoxide ion. Nomenclature will be briefly
covered, you are responsible to learn it on your own. ONL Y
BASIC NOMENCLA TURE. WILL BE ASKED ON THE EXAMS.
Steve Forsey, an instructor at Waterloo, is responsible for the
above advice and indicates that nomenclature is covered in
approximately the first two 50-minute lectures of Chem 266.
Students are expected to pick up the rest. Steve indicates that
beginning with nomenclature will have a tendency to scare the
students, which is a good thing because it gives students an
idea of the pace of this course. A good knowledge of
nomenclature would be beneficial for students since they could
focus more on the concepts rather than worry about the names of
compounds.
Literature cited
1. U. BDnzli-Trepp, Systematic Nomenclature of Organic, Organo-
metallic and Coordination Chemistry, CRC Press, Lausanne 2007.
2. R.B. Fox. W.H. Powell. Nomenclature of Organic Compounds.
Principles and Practice, 2nd edition, Oxford University Press, Oxford
2001.
3. Trivial and Semisystematic Names Retained for Naming Organic
Compounds. www.acdlabs.comliupac.n_omenclaturel931r93_671.htm
(accessed January 2009).
4. K.J. Thurlow. Chemical Nomenclature, Kluwer Academic Publishers,
Dordrecht, Boston 1998.
5. IUPAC Nomenclature of Organic Chemistry.
http://enwikipedia.orglwiki/lUPAC_nomeclature_o'-organic_chemistry
(accessed January 2009).
6. S. Skonieczny, Joumal of Chemical Education, 2006,83.1633-1637 .•
November 2009/Chem 13News 15