Chapter 3:

Alkanes and Their Stereochemistry

Functional Groups

• Functional groups are a group of atoms that has similar characteristic chemical behavior in every molecules where it occurs.

• Think of functional groups as individuals in a team. They bring their special abilities yet they all function as a unit or team.

• There are many functional groups with different properties.

Carbon – Carbon Functional Groups

• When a carbon is bound to a second carbon only 4 possibilities arise.

• Alkane – Carbon –Carbon (Single Bond - SP3)

• Alkene – Carbon – Carbon (Double Bond – SP2)

• Alkyne – Carbon – Carbon (Triple Bond – SP)• Arene – Carbon – Carbon (Aromatic Ring – Resonance Structures)

• Properties: Covalent Bonds (Oil Soluble)

Basic Carbon Structures: CarbonFamily Name Functional Group Simple Example Name Ending

Alkane -ane

Alkene

-ene

Alkyne

-yne

Arene

-none

C C

C C

C C

C CC

CCC

C C

H

H

H

H

HH

Ethane

Benzene

H

H

H

H

Ethene

C C HHEthyne

Carbon – Oxygen (Single Bond)

• When a carbon is singly bound to a oxygen the most common functional possibilities are:

• Alcohol (C-OH) are used as antiseptic, beverage, etc …• Ether (C-O-C) are used as solvents for synthesis.• Phosphate (C-O-PO3) found in DNA, RNA, and many biological

molecules.

• Properties: Polar Covalent Bonds (Water Soluble)

Basic Carbon Structures: OxygenFamily Name Functional Group Simple Example Name Ending

Alcohol-ol

Ether -ether

Phosphate None None

C O H

C O C

C C

H

H

O H

H

H

H

Ethanol

C O P

O

O

O

C O C H

H

H

H

Methyl Ether

H

H

Carbon – Oxygen (Double Bond)

• When a carbon is doubly bound to a oxygen called a carbonyl the most common functional possibilities are:

• Aldehyde C-(C=O)-H• Ketone C-(C=O)-C• Carboxylic Acid C-(C=O)-O-H• Carboxylic Acid Ester C-(C=O)-O-C• Carboxylic Acid Anhydride C-(C=O)-O-(C=O)-C

• Properties: Polar Covalent Bonds (Water Soluble)• Carboxylic Acid is a strong acid

Basic Carbon Structures: Carboxyl

Family Name Functional Group Simple Example Name Ending

Carboxyl

Aldehyde -al

Ketone -one

Carboxylic acid -oic acid

Ester -oate

Carboxylic acid anydride

-oic anhydride

C

O

C C

O

H

C C

O

C

C C

O

O H

C C

O

O C

C C

O

O C

O

C

H C

H

H

C

O

O H

Acetic Acid

Carbon – Nitrogen

• When a carbon is singly bound to a nitrogen the most common functional possibilities are:

• Amine- (C-N) single bond• Imine- (C=N) double bond• Nitrile (C=N) triple bond• Nitro (C-NO2)

• Amide (C=O)-N- • Properties: Polar Covalent Bonds (Water Soluble)• Can be strongly basic (accepts a proton)

Basic Carbon Structures: NitrogenFamily Name Functional Group Simple Example Name Ending

Amine -amine

Nitrile -nitrile

Nitro -none

Amide -amide

C N

C C N

C NO

O

C C

O

N

Carbon – Sulfur

• When a carbon is singly bound to a sulfur the most common functional possibilities are:

• Thiol (C-S-H) single bond to carbon and one to hydrogen• Sulfide (C-S-C) 2 single bond to carbon(s) • Sulfoxide C-(S=O)-C double bond• Sulfone C-(O=S=O)-C 2 double bonds • Properties: Polar Covalent Bonds (Water Soluble)

Basic Carbon Structures: SulfurFamily Name Functional Group Simple Example Name Ending

Sulfide sulfide

Sulfoxide sulfoxide

Sulfonesulfone

Thiol -thiol

C S C

C S

O

C

C S

O

C

O

C S H

Common Functional GroupsFamily Name Functional Group Simple Example Name Ending

Ether -ether

Amine

-amine

Carboxyl -

Arene

-noneC C

CCC

C

C O C

C N

C

O

Basic Carbon Structures: Alkane

C C

Basic Carbon Structure: Alkene

C C

Basic Carbon Structure: Alkyne

C C

Basic Carbon Structure: Alcohol

C O H

Basic Carbon Structure: Ether

C O C

Basic Carbon Structure: Carboxyl

• Carboxyl is found in a number of functional groups.

• It is reactive and is often used in organic reactions.

C

O

Basic Carbon Structure: Aldehyde

C C

O

H

Basic Carbon Structure: Ketone

C C

O

C

Basic Carbon Structure: Carboxylic Acid

C C

O

O H

Basic Carbon Structure: Ester

C C

O

O C

Basic Carbon Structure: Amine

C N

Basic Carbon Structure: Imine

C C N

Basic Carbon Structure: Nitrile

C C N

Basic Carbon Structure: Nitro

C NO

O

Basic Carbon Structure: Amide

C C

O

N

Basic Carbon Structure: Sulfide

C S C

Basic Carbon Structure: Sulfoxide

C S

O

C

Basic Carbon Structure: Sulfone

C S

O

C

O

Basic Carbon Structure: Thiol

C S H

What are Alkanes?

• Alkanes are chains of carbon(s) and hydrogen(s) that are SP3 hybridized.

• Remember: Carbon and hydrogen maintain similar electronegativies so that they have a covalent bond (even distrubtion of electrons). Non-polar molecules.

Properties of Alkanes

• Alkane chains are nonpolar molecules single bonded (SP3) carbon chains. You can think of them as oils.

• Alkanes are saturated hydrocarbon (also aliphatic) because they only contain carbons and hydrogens.

• Octane is an alkane chain of 8 carbons and 18 hydrogens that you use as fuel in your gas tank.

• Cooking oils are also alkane chains.

Types of Alkane Chains

• There are two different types of alkane chains.1) Straight chain alkanes (normal alkanes)

C C

H H

H

H

H

C

H

H

C

H

C

H

H

C

H

H

C

H

H

C

H

H

H

C

H

H

C

H

H

H

2) Branched-chain alkanes

C C

C

H

H

H

H

C

H

H

C

H

C

H

C

H

H

C

H

H

C

H

H

H

C

H

H

C

H

H

H

H

C

H

H

H

H

H

Different Structures that Represent Alkanes

CC

CC

HH

HH H

H HHH

H

CH3CH2CH2CH3

CH3(CH2)2CH3

CH3-CH2-CH2-CH3

C

H

H

C

H

H

C

H

H

C

H

H

HH

All of these structures represents C4H10 butane

Alkane Isomers

• Isomers are compounds that have the same number and kind of atoms but are arranged differently. They can be applied to most organic structures.

• Constitutional Isomers – have the same molecular formula but have different arrangements. See below (C4H10)

CH3CHCH3

CH3CH3CH2CH2CH3

They both have the same number of carbons and hydrogens.

Naming Carbon Backbones

• To name carbon chains we determine the number of the longest connected carbons to get a proper name.

• For example if we had a 5 carbon chain we would have Pent-

• And if the carbon chain were all single bonds we would have an –ane ending.

• The Name would be :Pentane

CH3CH2CH2CH2CH3 or

Naming Carbons Skeletons• 1 (Carbon) Meth-• 2 (Carbons) Eth-• 3 (Carbons) Prop-• 4 (Carbons) But- • 5 (Carbons) Pent-• 6 (Carbons) Hex-• 7 (Carbons) Hept-• 8 (Carbons) Oct-• 9 (Carbons) Non-• 10 (Carbons) Dec-

C

H

H

H H

C C

H H

H

H

H

H

C C

H H

H

H

H

C

H

H

H

C C

H H

H

H

H

C

H

H

C

H

H

H

C C

H H

H

H

H

C

H

H

C

H

C

H

H

H

H

C C

H H

H

H

H

C

H

H

C

H

C

H

H

C

H

H

H

H

C C

H H

H

H

H

C

H

H

C

H

C

H

H

C

H

H

C

H

H

H

H

C C

H H

H

H

H

C

H

H

C

H

C

H

H

C

H

H

C

H

H

C

H

H

H

H

C C

H H

H

H

H

C

H

H

C

H

C

H

H

C

H

H

C

H

H

C

H

H

H

C

H

H

H

C C

H H

H

H

H

C

H

H

C

H

C

H

H

C

H

H

C

H

H

C

H

H

H

C

H

H

C

H

H

H

Methane

Ethane

Propane

Butane

Pentane

Hexane

Heptane

Octane

Nonane

Decane

Carbons as Substitutents

• If carbon chains are part of a branched alkane chain then the branches would be the same parent (backbone) name but you would add a –yl to the end of the name.

• Methyl• Propyl• Octyl• Decyl

Naming Carbon Chains (Alkyl)

Prefix – Locant – Parent – SuffixHow many carbons are in the longest chain.

What is the primary group functional group.

Where is the primary group (number).

Additional functional groups and placements.

Steps to Naming Alkane Chains• Step 1. Find the longest carbon chain (Parent hydrocarbon).

YOU HAVE TO REALLY LOOK.

• Step 2. Number the atoms in the main chain. Make sure that if anything is bound to this chain it is at the lowest carbon number.

• Step 3. Identify and number the substitutents.

• Step 4. Write the name as a single word. Use hyphens to separate the groups and comma for the numbers.

• Step 5. Name a complex substitutents as though it were itself compound.

Example 1

C C

H H

H

C

H

C

H

H

C

C

C

H

H

H

H

H

H

H

H H

CH

H

H

C C

H H

H

C

H

C

H

H

C

C

C

H

H

H

H

H

H

H

H H

CH

H

H

C C

H H

H

C

H

C

H

H

C

C

C

H

H

H

H

H

H

H

H H

CH

H

H1

2

34567

Find the longest carbon chain

By counting carbons.

Seven carbons - Hept

Identify the number and name of the substitutents

Methyl on 3 carbon

Number the carbons in the chain substitutents with the lowest number.

C C

H H

H

C

H

C

H

H

C

C

C

H

H

H

H

H

H

H

H H

CH

H

H1

2

34567

C C

H H

H

C

H

C

H

H

C

C

C

H

H

H

H

H

H

H

H H

CH

H

H1

2

34567

Write the name on one line

3-Methylheptane

Types of Carbons

CHR

HHC

RR

HHC

RR

HRC

RR

RRPrimary Carbon (1o) Secondary Carbon (2oC) Tertiary Carbon(3o) Quarternany Carbon(4o)

These are the types of SP3 carbons, Primary, Secondary, Tertiary, Quaternary carbons.

Other Branched Alkane Group Names

CHH3C CH3

Isopropyl

CH2

HC

CH3

Isobutyl

CH3CH3-CH2-CH2-CH2- CH3-CH2-CH-CH3

Sec-ButylButyl

C CH3H3C

CH3

tert-Butyl(t-butyl)

3-carbons

4-carbons

CH3-CH-CH2-CH2-

Isopentyl, isoamyl

CH3

5-carbons

Properties of Alkanes

• Alkanes are normally chemically inert (normally does not easily react with anything except with O2)

• Both the melting point and boiling point increases with the length of the carbon chain.

• Increased branching decrease the boiling point when compared to the straight chains.

Conformation of Ethane• Stereochemistry is the

branch of chemistry that is concerned with the three dimensional aspects of molecules.

• Carbons that are singly bond rotate in space (just like an umbrella).

H

H H

H

H H

H

HH

H

HHH

H HH

HH

H

H H

H

HH

Newman Projections

Sawhorse Representation

Newman Projections looks directly down the carbon – carbon bond.

Torsional Strain

• Torsional Strain describes how atoms or groups move between single bonds as they rotate.– When 2 atoms or groups overlap then the energy

increases (eclipsed), when they move apart (staggered) the energy decreases.

– This happens three times in a rotation of 360o.

Conformation Energies• Energies of Ethane changes

not only in the staggered and eclipsed forms but with the size of the additional groups bound.

• The bigger the groups the more energy it takes to pass each other when rotating.

• The lowest energy called the anti-conformation places the two bulk groups on the other side of the bond.

H H

H H

HHHH

H H

HH

H H

HH

Newman Projections

Sawhorse Representation

Take Home Message

• Know Functional Groups• Know Naming of Alkanes• Know Properties of Alkanes• Understand Conformation and its Energies.