IUPAC Nomenclature Organic Compounds (Part 1) of

I. Introduction Carbon is special because a single carbon atom is capable of combining with up to four other atoms (valence of four = maximum of four bonds). Carbon can combine with many other carbon atoms making large molecules. This means that carbon atoms can form chains and rings onto which other atoms can be attached. In Chemistry, an organic compound is one containing carbon atoms.

I. Chains of Carbon Atoms The simplest Organic compounds are made up of only carbon and hydrogen atoms only and are called hydrocarbons. Names of simple chains of hydrocarbons are given names based on the number of carbon atoms in the molecule. Prefixes are used to denote the number carbon atoms. Alkane hydrocarbons consist of carbon and hydrogen atoms linked together with single bonds.

Cmethane C-Cethane C-C-Cpropane C-C-C-Cbutane C-C-C-C-Cpentane C-C-C-C-C-Chexane C-C-C-C-C-C-Cheptane I. Alkane Hydrocarbons

C-C-C-C-C-C-C-Coctane C-C-C-C-C-C-C-C-Cnonane C-C-C-C-C-C-C-C-C-Cdecane C-C-C-C-C-C-C-C-C-C-Cundecane C-C-C-C-C-C-C-C-C-C-C-Cdodecane

I. Alkyl Groups Attached to Chain methyl ethyl propyl butyl CH 3 CH 2 CH 3 CH 2 CH 3 CH 2 CH 3 CH 2

II. Structural Isomers Two or more compounds are structural isomers if they have the same formula but different connected structures. Structural isomers will have different IUPAC names (covered later). The alkane, C 4 H 10, has two structural isomers. Question #1: Try to build two different molecules with 4 carbons and 10 hydrogens (using only single bonds), then draw it. Hint: Use branching alkyl groups!!!!!!!!

C 4 H 10

C 4 H 10 has the following two structural isomers: C CH 3 CH 2 CH 3 CH 2 CH 3 H Note: Both molecules look different but have the same number of carbon and hydrogen atoms.

The following two molecules are exactly the same: C CH 3 H C H They are not different isomers! Build both molecules and try rotating one to match the other one.

Question #2: Try to build three different molecules with 5 carbons and 12 hydrogens (using only single bonds), then draw it. Hint: Use branching alkyl groups!!!!!!!! The alkane, C 5 H 12, has three structural isomers.

C 5 H 12

C 5 H 12 has the following three structural isomers: C CH 3 CH 2 CH 3 CH 2 CH 3 CH 2 H Note: All molecules look different but have the same number of carbon and hydrogen atoms. CH 3 C

C CH 2 CH 3 CH 2 CH 3 CH 2 H All of these compounds have the formula, C 5 H 12. We can only distinguish them by giving them different names. CH 3 C

III. Naming & Drawing Alkanes Parent Name = longest continuous chain of carbon atoms Name of branching group or substitute (if any) Parent name + General Formula: C n H 2n+2 Use Greek prefixes to indicate the presence of multiple identical branching groups.

CCCCCCC What is the parent name?

CCCCCCC Hexane (Longest chain is 6 carbons)

CCCCCCC What is the parent name? Hexane (Longest chain is 6 carbons)

CCCCCCC What is the parent name? Hexane (Longest chain is 6 carbons) What is the branching group? Methyl -CH 3

CCCCCCC What is the position of the methyl group? Must number carbon atoms so that the methyl group is attached to the carbon with the lowest number.

CCCCCCC What is the position of the methyl group? Must number carbon atoms so that the methyl group is attached to the carbon with the lowest number

CCCCCCC What is the name of the compound? 3-methylhexane Indicates position of alkyl group (substituent)

CCCCCC What if there are 2 or more of the same substituent? Use Greek prefixes to tell how many. E.g di, tri, tetra CC ,3-dimethylhexane Must use 3 twice because there are 2 methyl groups

CCCCCC CC C What is the longest chain? What are the substituents?

CCCCCC CC C What is the longest chain? Hexane What are the substituents? Methyl -CH 3 and Ethyl -CH 2 -CH 3

CCCCCC CC C What is the longest chain? Hexane What are the substituents? Methyl -CH 3 and Ethyl -CH 2 -CH 3

CCCCCC CC C Which substituent is named first? Answer: alpha order or by increasing size If by alpha order: Ethyl -CH 2 -CH 3 first If by size: Methyl -CH 3 first (smaller than ethyl)

CCCCCC CC C If by alpha order: 3-ethyl-3-methylhexane If by size: 3-methyl-3-ethylhexane

Practice Questions

CCCC Question 1: What is the correct IUPAC name?

CCCC Answer: butane

CH 2 CH 3 Question 2: What is the correct IUPAC name? CH 3

CH 2 CH 3 Question 2: What is the correct IUPAC name? Answer: propane CH 3

CCC C C Question 3: What is the correct IUPAC name? C

CCC C C C Answer: 2, 2-dimethylbutane

C CH 3 Question 4: What is the correct IUPAC name? CH 2 CH 3 CH 2 CH 3 CHCH 2 CH 3 CH 2 CH 3

C Question 4: What is the correct IUPAC name? CH 2 CH 3 CH 2 CH 3 CHCH 2 CH 3 CH 2 CH 3 Answer: 3,3–dimethyl-5-ethyloctane 35

Question 5: Draw the correct structural formula? 2-methylbutane

CH CH 3 Question 5: Draw the correct structural formula? CH 2 CH 3 Answer: 2 2-methylbutane or CH 2 CH 3 CHCH 3 2

IV. Naming & Drawing Cyclic Alkanes Parent Name = longest continuous chain of carbon atoms Cyclo = parent chain forms a ring Name of branching group or substitute (if any) Parent name+ General Formula: C n H 2n+2 + Use Prefix “cyclo”

H2CH2CCH 2 What is the parent name?

H2CH2CCH 2 What is the parent name? Propane (Longest chain is 3 carbons) Is the parent chain in a ring?

H2CH2CCH 2 What is the parent name? Propane (Longest chain is 3 carbons) Is the parent chain in a ring? Yes Correct name is:

H2CH2CCH 2 What is the parent name? Propane (Longest chain is 3 carbons) Is the parent chain in a ring? Yes Correct name is: cyclopropane

H2CH2CCH CH 2 CH 3 Parent name is cyclopropane. What is the branching group? Methyl –CH 3 Correct name is: methylcyclopropane Note: The number (1) is not needed to identify the place of the substituent if only one is present in the molecule.

H2CH2CCH H2CH2C CH 3 CHCH 3 Parent name is cyclobutane. What is the branching group? Methyl –CH 3 Correct name is: 1, 2-dimethylcyclobutane Note: The first named substituent is arbitrarily given the number one (1) position

There are several ways to draw structural formulae of cyclic compounds: H2CH2CCH 2 H2CH2C CC CC Each corner represents a carbon atom

Assignment #1: Multimedia Organic Chemistry Program Quiz – Introduction to Organic Alkanes Cycloalkanes