nomenclature of organic compounds (iupac)

NOMENCLATURE OF ORGANIC COMPOUNDS

Prepared by:

MR. LEXTER C. SUPNET

MAED-Physics

REVIEW

FRIEDRICH WÖHLER (1828) – set out to synthesize ammonium cyanate, NH4OCN, as in the

reaction

AgOCN(s) + NH4Cl(aq) AgCl(s) + NH4OCN(aq)

The white crystalline solid he obtained from the solution had none of the properties

of ammonium cyanate, even though it had the same composition. The compound was not

NH4OCN but (NH2)2OCN – urea, an organic compound.

As Wöhler excitedly reported to J.J. Berzulius, “I must tell you that I can make urea

without the use of kidneys, either man or dog, Ammonium cyanate is urea.”

Δ

REVIEW

ORGANIC CHEMISTRY – the branch of chemistry concerned with the compounds of carbon:

originally confined to the compounds produced by living organism but now extended to

include man-made substances based on carbon, such as plastics.

(Collins English Dictionary – Complete & Unabridged 2012 Digital Edition)

Carbon is singled out for special study because of the ability of C atoms to form strong

covalent bonds with one another allows them to join together into straight chains, branched

chains, and rings.

REVIEW

Organic compounds – contain carbon and oxygen atoms or carbon and hydrogen in combination

with a few other types of atoms, such as oxygen, nitrogen, and sulfur.

Hydrocarbons– simplest organic compound which consists of Carbon and Hydrogen atoms.

Methane (Ch4) – the simplest organic compound.

ISOMERS

ISOMERS – compounds that have the same molecular formula but differs in structural formula.

TYPES:

1. SKELETAL ISOMERS

2. POSITIONAL ISOMERS

3. FUNCTIONAL ISOMERS

4. STEREOISOMERS

5. GEOMETRICAL ISOMERS

SKELETAL ISOMERS

Skeletal isomers are constitutional isomers that have the same functional groups but differ

from each other in the connectivity of the carbon skeleton.

EXAMPLE 1: IDENTIFYING ISOMERS

Write structural formulas for all the possible isomers with the molecular formula C5H12.

Solution:

1. Write the longest chain of C atoms from left to right. This gives the straight-chain formula labeled (1).

To finish this structure, we add an appropriate number of H atoms (12, in this case) to give each C

atom four bond.

H H H H H

H C C C C C H

H H H H H

(1)

EXAMPLE 1: IDENTIFYING ISOMERS2. Now, look for isomers with four C atoms in the longest chain and one C atom as a branch (five C atom in all). There is only one possibility.

C

C C C C

(2)

Again, we complete the structure of this isomer by adding H atoms.

H

H C H

H H H

H C C C C H

H H H H

EXAMPLE 1: IDENTIFYING ISOMERS

3. Finally, let’s consider a three-carbon chain with one-carbon branches. Again, there is only

one possibility.

C CH3

C C C that is, CH3 C CH3

C CH3

(3)

The number of isomers with the formula C5H12 is three.

ISOMERS OF C5H12

H H H H H

H C C C C C H

H H H H H

(1)

CH3

CH3 C CH3

CH3

(3)

H

H C H

H H H

H C C C C H

H H H H

(2)

(1) (2) (3)

PRACTICE

Write the condensed structural formula for the five possible isomers with the formula C6H16.

ANSWERS:

1. CH3CH2CH2CH2CH2CH2CH3

2. (CH3)2CHCH2CH2CH3

3. CH3CH2CH(CH3)CH2CH3

4. (CH3)2CHCH(CH3)2

5. (CH3)3CCH2CH3

POSITIONAL ISOMERISMA variety of atoms or groups of atoms can be substituents on carbon chains, for

example, Br. The three monobromopentanes possess the same carbon skeleton. Because they

differ in the position of the bromine atom of the carbon chain, these structural isomers are

also called positional isomers.

1-Bromopentane 2-Bromopentane 3-Bromopentane

CH3CH2CH2CH2CH2Br CH3CH2CH2CH2CHCH3

Br

CH3CH2CHCH2CH3

Br

Br Br

Br

Br Br

Br

NOMENCLATURE

Early organic chemists often assigned names related to the origin or properties of

new compounds. Some of these names are still in common use. Citric acid if found in citrus

fruit; uric acid is present in urine; formic acid is found in ants (from the Latin word for ant,

formica); and morphine induces sleep (from Morpheus, the ancient Greek god of sleep). As

thousands upon thousands of new compounds were synthesized, it became apparent that a

system of common names was unworkable. Following several interim systems, one

recommended by the International Union of Pure and Applied Chemistry (IUPAC) was adopted.

RULES IN NAMING ORGANIC COMP0UNDS1. Select the longest continuous carbon chain in the molecule, and use the hydrocarbon name of

this chain as the base name. Except for the common names methane, ethane, propane, andbutane, standard Greek prefixes relate the name to the number of C atoms in the chain, as inpentane (C5), hexane (C6), heptane (C7), octane (C8),…

2. Consider every branch of the main chain to be substituent derived from another hydrocarbon.For each of these substituents, change the ending of its name from ane to yl. That is, the alkanesubstituent becomes alkyl group.

3. Number the C atoms of the continuous base chain so that the substituents appear at the lowestnumber possible.

4. Name each substituent according to its chemical identity and the numbers of the C atom towhich it is attached. For identical substituents use di, tri, tetra, and so on, and write theappropriate carbon number for each substituent.

5. Separate the numbers from one another by commas, and from letters by hyphens.

6. List the substituents alphabetically by name.

SOME COMMON ALKYL GROUPSNAME STRUCTURAL FORMULA

Methyl CH3

Ethyl CH2CH3

Propyla CH2CH2CH3

Isopropyl CH3CHCH3

Butyla CH2CH2CH2CH3

Isobutyl CH3

CH2CHCH3

s-butylb CH3CHCH2CH3

t-butylc CH3

CH3CCH3

aIn the past, the prefix normal or n- was used for a straight-chain alkyl group, such as n-propyl or n-butylbs = secondaryCt = tertiary

ORGANIC COMPOUNDS AND THEIR FUNCTIONAL GROUPS

Functional Groups – a specific region in an organic molecule that determines its chemical

properties.

EXAMPLE: NAMING AN ALKANE HYDROCARBON

Give an appropriate IUPAC name for the following compound, an important constituent of

gasoline.

CH3 CH3

CH3 C CH2 CH CH3

CH3

Solution:

The C atoms are numbered in red, and the side-chain substituents to be named are shown in

blue. The longest chain of C atoms is five, and the carbons are numbered so that the one with

two substituent groups is number 2, instead of number 4. Each substituent is a methyl group, -

CH3. Two methyl groups are on the second C atom, and one methyl group is on the fourth C

atom. The correct name is

2,2,4-trimethylpentane

1 2 3 4 5

PRACTICE: NAMING AN ALKANE HYDROCARBON

Give an appropriate IUPAC name for the following hydrocarbons:

A. CH3CH2CH(CH3)CH2CH2C(CH3)2CH2CH2CH3

B. CH3CH2CH(CH3)CH2CH2CH(CH3)CH2CH3

ANSWER:

A. 3,3,6-trimethylnonane

B. 3,6-dimethyloctane

EXAMPLE: WRITING THE FORMULA Write a condensed structural formula for 4-t-butyl-2-methylheptane.

SOLUTION:

A. Because the compound is heptane, the longest chain of C atoms is seven.

C C C C C C C

B. Starting from the left, we attach a methyl group to the second C atom.

CH3

C C C C C C C

C. Next, we attach a t-butyl group to the fourth C atom.

CH3

CH3 C CH3

CH3

C C C C C C C

D. Finally we add the remaining hydrogen atoms to give each C atom four bonds.

CH3

CH3 C CH3

CH3

CH3 CH CH2 CH CH2 CH2 CH3

PRACTICE

Write the condensed structural formula of the following:

• 3-ethyl-2, 6-dimethylheptane

• 3-isopropyl-2-methylpentane

Answer:

• CH3CH(CH3)CH(CH2CH3)CH2CH2CH(CH3)CH3

• CH3CH(CH3)CH[CH(CH3)2]CH2CH3

ALKANE

Class

GeneralStructural Formula Example

Name of Example

Alkane R H CH3CH2CH2CH2CH2CH3 Hexane

*The functional group is shown in red, R stands for an alkyl group

Exercise: Give the appropriate IUPAC name of the alkane CH3CH2CH2CH2CH3

Ans: Pentane

ALKENE

Class


Name of Example

Alkene C C CH2 CHCH2CH2CH3 1-Pentene


Exercise: Give the appropriate IUPAC name of the alkene CH3CH CH2CH2CH2CH2CH3

CH3CH2CH2C CH2

CH2CH3

Ans: 2-heptene

2ethy,1-pentene

ALKYNE

Class


Name of Example

Alkyne C C CH3C CCH2CH2CH2CH2CH3 2-Octyne


Exercise: Give the appropriate IUPAC name of the Alkyne CH3CHC CCH3

CH3

Ans: 4-methy,2-pentyne

ALCOHOL

Class


Name of Example

Alcohol R OH CH3CH2CH2CH2CH2OH 1-Butanol


Exercise: Give the appropriate IUPAC name of the alcohol CH3CH2OH

Ans: Methanol

ALKYL HALIDE

Class


Name of Example

Alkyl halide R X** CH3CH2CH2CH2CH2CH2CH2Br 1-Bromohexane


**X stands for a halogen atom – F, Cl, Br, I

Exercise: Give the appropriate IUPAC name of the alkyl halide CH3CH(Cl)CH2CH3

Ans: 2-chlorobutane

ETHER

Class


Name of Example

Ether R O R CH3 O CH2CH2CH3 1-Methoxypropane(methyl propyl ether)



Exercise: Give the appropriate IUPAC name of the ether CH3CH2OCH2CH3

Ans: diethyl ether

AMINE

Class


Name of Example

Amine R NH2 CH3CH2CH2 NH2 1-Aminopropane(propylamine)



Exercise: Give the appropriate IUPAC name of the amine

CH3CH(NH2)CH2CH2CH3

Ans: 2-Aminopentane

ALDEHYDE

Class


Name of Example

Aldehyde O

R C H

O

CH3CH2CH2C H

Butanal(butyraldehyde)


Exercise: Give the appropriate IUPAC name of the aldehyde H2C O

Ans: Methanal (formaldehyde)

KETONE

Class


Name of Example

Ketone O

R C R

O

CH3CH2CH2CCH2CH3

3-Hexanone(ethyl propyl ketone)


Exercise: Give the appropriate IUPAC name of the ketoneO

CH3CCH3

Ans: Propanone (Acetone)

CARBOXYLIC ACID

Class


Name of Example

Carboxylic acid

O

R C OH

O

CH3CH2CH2C OH

Butanoic acid(butyric acid)


Exercise: Give the appropriate IUPAC name of the Carboxylic acidO

HC OH

Ans: Methanoic acid (formic acid)

ESTER

Class


Name of Example

Ester O

R C OR

O

CH3CH2CH2C OCH3

Methyl butanoate(methyl butyrate)


Exercise: Give the appropriate IUPAC name of the esterO

HOC OCH3

Ans: Methyl methanoate

AMIDE

Class


Name of Example

Amide O

R C NH2

O

CH3CH2CH2C NH2

Butanamide(butyramide)


Exercise: Give the appropriate IUPAC name of the amideO

CH3CH2C NH2

Ans: Propanamide

ARENE

Class


Name of Example

Arene Ar H**

CH2CH3

Ethylbenzene


**Ar stands for aromatic (aryl) group such as the benzene ring

Exercise: Give the appropriate IUPAC name of the arene

CH3CH2 CH3

Ans: 1-ethyl,4-methylbenzene

ARYL HALIDE

Class


Name of Example

Aryl halide Ar X**

BrBromobenzene



***X stands for halogen atom – F, Cl, Br, I

PHENOL

Class


Name of Example

Phenol Ar OH**

Cl OH4-Chlorophenol



***X stands for halogen atom – F, Cl, Br, I

Exercise: Give the appropriate IUPAC name of the phenolCH3

OHAns: 2-methylphenol

THANK YOU!

REFERENCES

• PETRUCCI, R.H., HARDWOOD, W.S., HERRING, F.G. 2002. General Chemistry: Principles and

Modern Applications. 8th Edition. Pearson Education South Asia Pte. Ltd. Singapore.

• Collins English Dictionary – Complete & Unabridged 2012 Digital Edition

• http://science.uvu.edu/ochem/index.php

http://science.uvu.edu/ochem/index.php

nomenclature of organic compounds (iupac)

Education

c ch3 c c c

ability of c atoms

appropriate number of

longest chain of c atoms

ch3c ch3 c ch3

compounds of carbon

carbon chains

carbon skeleton