Organic Compounds (Part 1) IUPAC Nomenclature of Organic Compounds (Part 1)

I. Introduction In Chemistry, an organic compound is one containing carbon atoms. 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.

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.

I. Alkane Hydrocarbons C methane C-C ethane C-C-C propane C-C-C-C butane C-C-C-C-C pentane C-C-C-C-C-C hexane C-C-C-C-C-C-C heptane

C-C-C-C-C-C-C-C octane C-C-C-C-C-C-C-C-C nonane C-C-C-C-C-C-C-C-C-C decane C-C-C-C-C-C-C-C-C-C-C undecane C-C-C-C-C-C-C-C-C-C-C-C dodecane

I. Alkyl Groups Attached to Chain methyl CH2 CH3 ethyl propyl CH2 CH2 CH3 butyl CH2 CH2 CH2 CH3

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, C4H10 , 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!!!!!!!!

C4H10

C4H10 has the following two structural isomers: Note: Both molecules look different but have the same number of carbon and hydrogen atoms.

The following two molecules are exactly the same: CH3 H CH3 C CH3 CH3 C CH3 H CH3 They are not different isomers! Build both molecules and try rotating one to match the other one.

The alkane, C5H12 , has three structural isomers. 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!!!!!!!!

C5H12

C5H12 has the following three structural isomers: Note: All molecules look different but have the same number of carbon and hydrogen atoms.

CH3 CH3 CH3 C CH3 CH3 C CH2 CH3 CH3 H CH3 CH2 CH2 CH2 CH3 All of these compounds have the formula, C5H12. We can only distinguish them by giving them different names.

III. Naming & Drawing Alkanes General Formula: CnH2n+2 Name of branching group or substitute (if any) Parent name + Parent Name = longest continuous chain of carbon atoms Use Greek prefixes to indicate the presence of multiple identical branching groups.

C C C C C C What is the parent name? C

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

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

C C C C C C C What is the parent name? Hexane (Longest chain is 6 carbons) What is the branching group? Methyl -CH3 C

C C C C C C C 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. C

C C C 3 C 2 C 1 4 3 C 4 5 6 5 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. 2 C 6 1

C C C C C C C 3 2 1 4 3 4 5 6 5 What is the name of the compound? 3-methylhexane 2 C 6 1 Indicates position of alkyl group (substituent)

C C C C C C C C 3,3-dimethylhexane What if there are 2 or more of the same substituent? Use Greek prefixes to tell how many. E.g di, tri, tetra C C C C C C 3 4 5 6 C 3,3-dimethylhexane 2 C Must use 3 twice because there are 2 methyl groups 1

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

C C C C C C C C C What is the longest chain? Hexane What are the substituents? Methyl -CH3 and Ethyl -CH2 -CH3

C C C C C C C C C What is the longest chain? Hexane What are the substituents? Methyl -CH3 and Ethyl -CH2 -CH3

C C C C C C C C C Which substituent is named first? Answer: alpha order or by increasing size C C If by alpha order: Ethyl -CH2 -CH3 first If by size: Methyl -CH3 first (smaller than ethyl)

C C C C C C C C C 6 5 4 3 If by alpha order: 3-ethyl-3-methylhexane If by size: 3-methyl-3-ethylhexane C C 2 1

Practice Questions

Question 1: What is the correct IUPAC name?

Question 1: What is the correct IUPAC name? Answer: butane

Question 2: What is the correct IUPAC name? CH3 CH2 CH3

CH3 CH2 CH3 Question 2: What is the correct IUPAC name? Answer: propane

Question 3: What is the correct IUPAC name?

C C C C C C Question 3: What is the correct IUPAC name? Answer: 2, 2-dimethylbutane

CH3 CH3 C CH2 CH CH2 CH3 CH3 CH2 CH2 CH2 CH3 Question 4: What is the correct IUPAC name? CH3 CH3 C CH2 CH CH2 CH3 CH3 CH2 CH2 CH2 CH3

CH3 CH3 C CH2 CH CH2 CH3 CH3 CH2 CH2 CH2 CH3 Question 4: What is the correct IUPAC name? CH3 CH3 C CH2 CH CH2 CH3 3 5 CH3 CH2 CH2 CH2 CH3 Answer: 3,3–dimethyl-5-ethyloctane

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

2-methylbutane CH3 CH2 CH CH3 CH3 CH3 CH3 CH CH2 CH3 Question 5: Draw the correct structural formula? 2-methylbutane 2 CH3 CH2 CH CH3 Answer: CH3 CH3 or CH3 CH CH2 CH3 2

IV. Naming & Drawing Cyclic Alkanes General Formula: CnH2n+2 Name of branching group or substitute (if any) Use Prefix “cyclo” + + Parent name Parent Name = longest continuous chain of carbon atoms Cyclo = parent chain forms a ring

CH2 H2C CH2 What is the parent name?

CH2 H2C CH2 What is the parent name? Propane (Longest chain is 3 carbons) Is the parent chain in a ring?

CH2 H2C CH2 What is the parent name? Propane (Longest chain is 3 carbons) Is the parent chain in a ring? Yes Correct name is:

CH2 H2C CH2 What is the parent name? Propane (Longest chain is 3 carbons) Is the parent chain in a ring? Yes Correct name is: cyclopropane

CH2 H2C CH CH3 Parent name is cyclopropane. What is the branching group? Methyl –CH3 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.

H2C CH CH3 3 2 H2C 4 1 CH CH3 Parent name is cyclobutane. What is the branching group? Methyl –CH3 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: H2C CH2 C C H2C CH2 C C Each corner represents a carbon atom

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