Organic Nomenclature - Chem 13 News

Nomenclature of organic compounds - Part I Stanislaw Skonieczny and Andrew P. Dicks Department of Chemist')'. University o(Toronto Toronto ON M5S 3H6 ...

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Nomenclature of organic compounds - Part I Stanislaw Skonieczny and Andrew P. Dicks Department of Chemist')'. University o(Toronto Toronto ON M5S 3H6 Introduction

2. Determine the parent hydrocarbon (principal chain or parent ring system containing the principal functional group).

Naming organic compounds is an important component of the Canadian high school chemistry curriculum.' However, high

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

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.

Abbreviations

and terminology

Used2

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.

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 established in Rule 4. 6. Assign stereochemistry atom(s) (stereocentres)

by numbering

where appropriate to chiral carbon 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-.

Nomenclature

of specific compound types

(i) Alkanes (CnH2n+2l The first four members of the series have semi-trivial names4

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.

Methane

Ethane

Propane

Butane

Systematic names of all other members of the series are formed

Substituent - functional group or atom that substitutes a hydrogen atom in the parent hydrocarbon.

by combining the ending "-ane" with the Greek (sometimes also the Latin) numerals indicating the number of carbon atoms in the

Substitutive Name - name indicating substitution of H atom(s) in the parent hydrocarbon.

chain.

Suffix - name of the principal functional group listed after the name of the parent hydrocarbon. Trivial Name - name without components of systematic

Pentane

Heptane

Hexane

meaning.

General guidelines for naming organic compounds Construction of the systematic name for an organic compound involves several steps, to be taken as far as applicable in the following order:

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.

1. Determine the principal functional group in the compound. When more than one functionality is present, the principal

-CH3

group is that which has highest precedence (see Table 1 in Part II). This group is cited as the suffix; all other groups are

Methyl

-CH~CH2CH3 Ethyl

Propyl

-CH2CH2CH2CH3 Butyl

cited as prefixes.3

October

2009/Chem 13 News 9

Branched Alkyl Groups

In naming unsaturated chains, the "-ane" ending of the corresponding saturated chain is changed to "-ene" (for one double

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

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.

-CH(CH3l2

-CH2CH(CH3l2

1-Methylethyl

lUPAC:

Retained Isopropyl trivial name:

-CH(CH3)CH2CH3

2

2-Methylpropyl

1-Methylpropyl

1,1-0imethylethyl

Isobutyl

sec-Butyl

lett-Butyl

(ii) Cycloalkanes

(CnH2n)

The prefix "cyclo" is a part of the name (capitalized and used to alphabetize ).

o o

D Cyclobutane

Cyclopentane

Cyclohexane

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

7

But-2-yne

double and triple bonds constitute functional

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. .. 1

rG

5

3

654

4

3

2-Methylhex-1-en-4-yne

(l)-2-Ethylpenta-1,3-diene

6 2

3'

2

4

of Unsaturated Hydrocarbons

1. Carbon-carbon

nearer a second substituent (and so on). The name of a branched hydrocarbon is composed of the parent chain name and substituent prefixes.

1

3

groups. 2. The parent hydrocarbon is that which contains the maximum number of multiple bonds. If more than one such chain is

Cycloalkanes are named by applying the prefix "cyclo" to the name of the alkane with the same number of carbon atoms.

Cyclopropane

2

Pentc1-ene Nomenclature

Note that italics are never capitalized and are omitted while alphabetizing substituents.

4

1~5

4

) .; )5

5

~ ~

4

5

1-Ethyl-3-methylcyclopentane

4-Ethyl-2-methylheptane

1Jl3

6U4

6

5

(3E,5E)-5-Methylhepta-3,5-dien-1-yne

(iii) Alkenes (CnH2n) and Alkynes ,(CnH2N-2) Some common unsaturated hydrocarbons

7

2

have retained trivial

(iv) Haloalkanes

2-Methylcyclohexa-1,3-diene

(formerly known as alkyl halides)

names6: Halogens (together with alkyl groups and a nitro group) are H2C=CH2

HC=CH

~

always named as substituents and listed as prefixes.9 6

BryZr IUPAC:

Ethene

2-Methylbuta-1,3-diene

Ethyne

Retained trivial name:

Ethylene

Isoprene

Acetylene

2U

4

1

5

3,3-Dibromocyclopentene

10 Chern 13 News/October

2009

1

M 3

CI

(E)-4-Chloro-2-methylhex -3-ene

(v) Aromatic Coml}()unch.

{i Trivial and Semisystematic

(il/r.llll/'.)

Compounds

HiUh

1I111il lllroCtlr.'1lll/l

Sd101Illoxlbo'llill

henzene aml.ll' (1""\1rtliv"'~1 :;"';lllnikyl

(accessed January 2009).

CllfllPlJlJlllls 10

0 1110111,1"': '

UlOllp". ""\iiIIlS.

nitro

7. RB. Fox, W.H. Powell. Nomenclature of Organic Compounds.

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

Names Retained for Naming Organic

www.acdlabs.comliupaclnomenclaturel93!r93_671.htm

Principles and Practice, 2nd edition, Oxford University Press, Oxford 2001.

1 Clndis

traditionally Ollllll"d !~l""fl IIlvllllllilllllll' or lTlonosubstituted aromatic COIllIHJlIIlIlr. ,'"1 1Illllllll1d Ily IUI'I\C Itl

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,

2)

/~l

l;/IJ IUPAC Retained trivial name

0/

6

~I

M"lhyll","Il"'"

1 M"lhvlulhylbunzene

Methoxybenzene

'Tolt""I"

Clunrmo

Anisole

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.

•

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.

&

r' l

IUPAC accepted

Br-C>-Br

1.2.Dlmt'lhylbenzene

1-Chloro-3-methylbenzene

1.4-Dibromobenzene

()- Xylem,

m-Chlorololuene

p-Dibromobenzene

When three or more substiluents

are present, only numbers can

be used. The lowest possible numbers are assigned. 6

li

1Br

SI

4

#2

CI

3

2-Ethyl-1,4-dimethylbenzene

1-Bromo-2-chloro-5-fluor0-4-methylbenzene

Nick Kim, www.//lab-initio.com/

References 1.

Pan-Canadian

Protocol Grade 11-12 Chemistry Specific Leaming

Outcomes. Council of Ministers of Education. Canada 2.

U BOnzli-Trepp. Systematic Nomenclature Organometallic

and Coordination

of Organic,

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 Oxford 1993.

1993. Blackwell Science.

Nomenclature of organic compounds - Part II Stanislaw Skonieczny and Andrew P. Dicks Department o/Chemistry, University o/Toronto, Toronto ON M5S 3H6 Introduction

Substituents are always listed as prefixes: CI

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.

Abbreviations

HO~

CI~1

3

2-Methylpropan-1-o1

n

34

OH

1

3

5-Bromo-2-methylcydohexan-1-o1

4.4-Dichlorobutan-2-ol

Examples when a multiple bond is present:

~

4\JOH

2 HO~

Alcohol - a compound in which a hydroxyl functional group (-OH), is attached to a saturated (sp3 hybridized) carbon atom.

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.

Br

6

and terms used1

Aryl Group - a group formed by a removal of a hydrogen atom from an aromatic ring carbon atom, abbreviated as Ar.

Ii

HO

3

3

IUPAC:

Prop-2-en-l-01

Prop-2-yn-1-o1

Retained trivial name:

Allyl alcohol

Propargyl alcohol

2

6-Methylcyclohex-2-en-1-o1

Dials The suffixes "-diol", "-triol", "-tetrao!", etc. are used for multipleOH groups. Contrary to nomenclature of alcohols, the terminal "-e" is retained in the name of parent hydrocarbon.

HO~

H0-o-0H

HO~OH

OH

Phenyl Group - CsHs-, abbreviated as Ph. Prefix - a substituent name listed before the parent

Ethane-1,2-diol

Benzene-1,4-diol

Propane-1,3-diol

hydrocarbon. Principal Functional Group - highest priority functional group (see Table 1).

Phenols

n 5

R - abbreviation used to represent an alkyl group. Suffix - name of the principal functional group listed after the name of the parent hydrocarbon.

Nomenclature

(

j-OH

HO~ 6

Phenol

of specific functional groups

~ I.

).

CI

3

1 OH

2

5

3-Chlorophenol

2-Methylphenol

(i) Alcohols

(ii) Ethers

The presence of a hydroxyl group (-OH) as the principal

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

functional group is indicated by the suffix" -01" replacing the terminal "-en in the parent hydrocarbon name. The longest

chain becomes the suffix of the ether name.

carbon chain is numbered so as to give the carbon bearing the hydroxyl group the lowest possible number. This number is used

-OCH3

to denote the position of the hydroxyl and is placed just before the suffix "-01". In the case of methanol and unsubstitlited

Methoxy

-OCH2CH2CH3 Propoxy

-OPh

-OCH2Ph

Phenoxy

ethanol, the locants are omitted.2

1

OH 2

3~OH Methanol

Benzyloxy

Propan-1-o1

/0, 3~1 Propan-2-o1

Methoxymethane

"'-../0, Methoxyethane (not ethoxymethane)

K oJ

4

2-Ethoxybutane

November 2009/Chem 13 News 13

0-/ '-0 ° ~ ~ II

II

O~6

Y0fo

0

H

IUPAC

Methoxybenzene

Ethoxybenzene

Ethoxyethene

Retained trh/iel name:

Anisole

Phenetole

Ethyl vinyl ether

IUPAC:

Benzenecarbaldehyde

Shorter name accepted by IUPAC:

Benzaldehyde

(v) Carboxylic

(iii) Ketones In general, ketones (R-CO-R) take the suffix "-one" with a fixed position number.

y

~

0 IUPAC: Retained trivial name'

1

3

6

2

7

2.6-0imethylhepta-2.5-dten-4-(lne

l-Phenylethan-1-(lne

Acetone

Phorone

Acetophenone

acids

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

}-Q

Propan-2-(lne

3-0xocyclopentanecarbaldehyde

OH

yOH O~CI

HoAo

0

2

3

IUPAC:

Methanoic acid

Ethanoic acid

3-Chloropropanoic

Retained trivial name:

Formic Acid

Acetic acid

3-Chloropropionic

acid acid

H

If a higher precedence suffix exists, the prefix "oxo-" is used:

HO

# 2

4

3

o

o

O')!-OH 5~OH O~_

o

3 IUPAC:

2-0xopropanoic

Retained trivial name:

Pyruvic

acid

acid

4-0xopentanoic Levulinic

IUPAC

(S)-2-Hydroxypropanoic

Retained trivial name:

Lactic acid

acid

acid

)=0

oA

H

OH

2,3-0ihydroxybutanedioic

acid

T arlanc acid

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

OH

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".4 The principal group assumes position 1.

acid

(iv) Aldehydes

H

1

0Y'"

HO~. O~

Br IUPAC:

Benzenecarboxylic

Retained trivial name'

Benzoic acid

acid

5-Bromo.2.hydroxycyclohexanecarboxylic

H (vi) Esters

IUPAC: Retained trivial name:

Methanal

Ethanal

Propanal

Formaldehyde

Acetaldehyde

Propionaldehyde

The suffix "-carbaldehyde':

is used when the -CHO group is

Esters (RCOOR') are named as alkyl derivatives of carboxylic acids. The alkyl (R') group is named first. The RCOOcomponent is then named as a separate word based on the carboxylic acid name, with the ending changed from "-oic acid" to "-oate".5

21~'

attached to the carbon atom of a ring. The name of the parent ring is retained in full.

3

14 Chem 13 News/November 2009

IUPAC:

Methyl

ethanoate

2-Methylpropyl

Retained trivial name:

Methyl

acetate

Isobutyl

propanoate

propionate

acid

Table 1. Decreasing

(vii) Amides

Functional 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

Order of Precedence

Functional

Suffix if Highest

Prefix if Lower

Group

Precedencea

Precedence

-(C)OOHb -eOOH

-carboxylic

-eOOR

alkyl carboxylate

Ethanamide

N.IY-O,methy1methanamlde

3,N.Dimethylbenzene<:artlo.amlde

-eONH2

Acetamide

N,N-Oimethytformamide

3.N-Dimethy1benzamide

-G=-N

IUPAC: Retained trivial name:

~

Ethanamine

Propan-1-amine

Butan-2-amine

Ethylamine

Propylamine

sec-Butylamine

carbamoyl-

-nitrile

cyano-

'N/'-...... H N-Methylethanamine

/

N

i

a

-01

hydroxy-

-NH2

-amine

amino-

>C=C<

-ene

*

-C=C-

-yne

** halo-, alky/-,

**"

alkoxy-, aryl-, nitro-

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.

N-Ethyl-N-methylpropan-1-amine

Editor's note

Always used as a suffix.

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.

formyl-

-QH

-Ar. -N02

\......../

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.

oxo-

-carbaldehyde

-X, -R, -OR,

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

-

oxo-

"-amine" with fixed position number. 5 HzN~

alkoxycarbonyl-

-one

Amines are named for the attached alkane chain with the suffix

>c=O

""""""'NHz

carboxy-

-earboxamide

-81

-eHO

NHz

acid

-amide

-(C)Hob

(viii) Amines

-

-oic acid

-(C)ONH2b

Retained trivial name:

for the Major

Groups6

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. Literature 1.

cited

U. BDnzli-Trepp,

Systematic Nomenclature

metallic and Coordination 2.

of Organic, Organo-

Chemistry, CRC Press, Lausanne 2007.

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

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

(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

.•

compounds.

November 2009/Chem 13 News 15