CHE 102 Chap 191

Chapter 19

Organic Chemistry: Saturated Hydrocarbons

CHE 102 Chap 192

Success!

• First two weeks is key to the 1st half of the semester• Need to build a framework for what we will cover

– Naming and Drawing molecules

– Physical properties (as a function of structure)

– Reactions

– Each category above is about 25% of each exam, the last 25% is miscellaneous concepts.

CHE 102 Chap 193

Organic Chemistry

• Study of compounds containing C, H, O, N (other trace elements – P, S, Halogens)

• Covalent Molecules

CHE 102 Chap 194

Lewis Structures (Review Ch 11)

• # bonds formed by C, H, O, N, Halogens

• Single, double, triple bonds

• Molecular geometry

CHE 102 Chap 195

Hybridization (Review Ch 10)

• Lewis Models Fail!• Required to explain differences in bond strength and

length

CHE 102 Chap 196

Hybrid Orbitals

• s + 3p -> sp3

• Sigma Bonds () = single bonds

CHE 102 Chap 197

Representing Organic Molecules

• Molecular Formula• Structural Formula

– Lewis structures• With electrons

• With bonds

• Condensed Formula– Assumes some knowledge of Lewis Structures/Bonding

• Line Models• R-groups

CHE 102 Chap 198

Functional Groups

• Organic compounds with similar structures are grouped into classes as shown in Table 19.1.

• The members of each class of compounds contain a characteristic atom or group of atoms called a Functional Group.

– is part of a larger molecule.– is composed of an atom or group of atoms that have characteristic

chemical behavior.– Chemically, a given functional group behaves in nearly the same

way in every molecule it’s part of.

• MEMORIZE the General Formula’s in Table 19.1

CHE 102 Chap 199

Functional Groups

CHE 102 Chap 1910

Functional Groups

CHE 102 Chap 1911

Functional Groups

CHE 102 Chap 1912

IUPAC System for Naming Organic Compounds

• The method recommended by the International Union of Pure and Applied Chemistry is systematic, generally unambiguous, and internationally accepted.

• Some trivial or common names are still used.

CHE 102 Chap 1913

Naming Alkanes

1. Select the longest chain = Main chain– All other chains = side chains

2. Number the carbon atoms in the parent carbon chain from one end to the other, starting at the end closest to the first carbon atom that has a branch chain.

3. Name each branch-chain alkyl group and designate its position on the parent carbon by a number.

• Multiple side groups use (di, tri, tetra, penta…)

• Name multiple different groups alphabetically

• Ties go in alphabetical order

CHE 102 Chap 1914

Naming the Main Chain

CHE 102 Chap 1915

Side Group NamesParent name, change –ane to -yl

CHE 102 Chap 1916

Special Side Groups

CHE 102 Chap 1917

Don’t Get Confused!

• The longest chain isn’t always straight• The longest chain isn’t always left to right, it can go

up/down or curve all around• Chain numbers don’t always go left to right• Always maximize the number of side chains• Ties go in alphabetical order

CHE 102 Chap 1918

Drawing Alkanes

1. Draw the main chain

2. Number the main chain, attach side chains.

CHE 102 Chap 1919

Alkyl halides or Haloalkanes

• Name like regular alkanes• Halogen = side chain

– F = fluoro

– Cl = chloro

– Br = bromo

– I = iodo

• The longest chain MUST contain the halogen.

CHE 102 Chap 1920

Isomers

• Compounds with:– Same Formula

– Different Structure

• The various individual compounds are called isomers.– e.g. There are two isomers of C4H10.

CHE 102 Chap 1921

Example of IsomersIt is possible to write two structural formulas corresponding to the molecular formula C4H10:

C C C

HH

H

H

H

H

C

H

H

H

H

butane or n-butanebp = -0.5 Cmp = -138.3 C

C C C

HH

H

H

C

H H

isobutanebp = -11.7 Cmp = -159.5 C

H

H

H

H

CHE 102 Chap 1922

How to Draw Isomers

• Start with parent compound:– Rip a carbon off, and attach it to the main chain (but not in

an end position)

– Move carbon along positions in chain• Only do ½ the molecule (otherwise its symmetrical/identical)

• Name molecules to double check you don’t duplicate them

– Rip off another carbon and repeat above until you can make no new structures.

CHE 102 Chap 1923

CHE 102 Chap 1924

Cycloalkanes

CHE 102 Chap 1925

Naming Cycloalkanes

• Main Chain– Just stick “cyclo” in front of it

• Side Chains– Single group (numbers not needed)

– 2+ Groups, number clockwise or counter clockwise to give the lowest set of numbers possible

CHE 102 Chap 1926

Hydrocarbons

Contain only C and H– aliphatic (do not contain benzene ring)

• alkanes, cycloalkanes

• (Ch 20) alkenes, alkynes

– aromatic (contain a benzene ring)• Ch 20

– An organic compound is classified as saturated if it contains only single bonds.

– An organic compound is classified as unsaturated if the molecules possess one or more multiple carbon-carbon bonds.

CHE 102 Chap 1927

Physical Properties

• Alkane molecules are non-polar.– Carbon-carbon bonds are non-polar, since they are between

like atoms.

– Carbon-hydrogen bonds are only slightly polar.

– Low polarity =>low boiling points

– Boiling point is a function of mass

CHE 102 Chap 1928

Physical Properties

CHE 102 Chap 1929

Reactions Involving Carbon (General)

• General– Oxidation/Reduction

– Substitution

– Elimination

– Addition

• Specific to Alkanes– Halogenation

– Dehydrogenation

– Combustion

CHE 102 Chap 1930

Recognizing Reactions

• Examine the products and reactants (classes)– Ex: Alkane + Halogen -> Alkyl Halide

– Ex: Alkane + O2 -> CO2 + H2O + Energy

• Examine the catalysts or reaction conditions

CHE 102 Chap 1931

Oxidation

When carbon atoms are oxidized, they often form additional bonds to oxygen.

H

CH H

H

+ 2 O2 O C O + 2H2O

CHE 102 Chap 1932

Reduction

When carbon atoms are reduced, they often form additional bonds to

hydrogen.H

CH OH

H

+ 3 H2O C O + H2O

CHE 102 Chap 1933

Substitution Reaction

If, in a reaction, one atom in a moleculeis exchanged by another atom or group ofatoms, a substitution reaction has takenplace.

H

CH H

H

+ Br2

H

CH Br

H

+ HBr

CHE 102 Chap 1934

Elimination Reaction

• An elimination reaction is a reaction in which a single reactant is split into two products, and one of the products is eliminated.

• Elimination reactions form multiple bonds.H

CC Br

H

+ HBrH

H

H

H

CC

H

H

H

CHE 102 Chap 1935

Addition Reaction

• Two reactants adding together to form a single product is called an addition reaction.

• An addition reaction can be thought of as the reverse of an elimination.

H

CC Br

H

+ HBr H

H

H

H

CC

H

H

H

CHE 102 Chap 1936

Reactions of Alkanes

• Combustion• Halogenation

– a substitution reaction

• Dehydrogenation – an elimination reaction

• Cracking – breaking up large molecules to form smaller ones

• Isomerization – rearrangement of molecular structures

CHE 102 Chap 1937

Combustion

Alkane + O2 CO2 + H2O + Heat/Energy

2 C3H6 + 9 O2 6 CO2 + 6 H2O + Heat/Energy

CHE 102 Chap 1938

Halogenation

CH3CH3 + Cl2 CH3CH2Cl + HCl

Alkane + X2 (F, Cl, Br, I) Alkyl Halide + HX

CHE 102 Chap 1939

CH3CH2CH3 CH3CH=CH2 + H2

Dehydrogenation

Heat

Alkane Alkene + H2

CHE 102 Chap 1940

Isomerization

CH3CH2CH2CH2CH3

catalyst,pressure,heat CH3CH2CHCH3

CH3

Cracking

C16H34 C8H18 + C8H16