Organic Chemistry

What is it?

• Study of compounds involving carbon

– Carbon has the ability to make chains and rings with itself

– Thousands of compounds contain only Carbon and Hydrogen

– Millions with other elements added

• Usually, Nitrogen, Oxygen, Sulfur, Halogens

Patterns

• Within the millions of compounds there are patterns that emerge

– Carbon forms 4 Bonds

– Hydrogen forms 1 Bond

– Oxygen forms 2 Bonds

– Halogens form 1 Bond

Identifying Compounds

• Name – Based on naming conventions (Usually IUPAC)

• Molecular Formula – Shows actual number of atoms present C4H8O2

• Empirical Formula – Shows the simplest whole number ratio of atoms C2H4O

• Structural Formula – Shows how the atoms are arranged CH3COCH2CH2OH

Cont.

• Graphical Formula – Shows how the atoms are arranged in space and bonded

• Similar to Lewis Structures but w/o the dots– CH3COCH2CH2OH

Cont.

• Skeletal Formula – Abbreviated form of graphical formula often omitting carbons and hydrogens CH3COCH2CH2OH

• Example – Draw the structural, graphical, and skeletal formula for C3H8

• Example – Draw the structural, graphical, and skeletal formula for C5H8O2

• Example – Draw the structural, graphical, and skeletal formula for C4H6

Homework

• Organic Worksheet #1

Alkanes• Straight chain organic compounds

containing only C, H, and sometimes halogens

• All carbons are sp3 hybridized• General formula CnH2n+2

• 1 C =

CH4

• 6 C’s =

C6H14

Properties

• Nonpolar – Dissolve other nonpolar compounds– Hydrophobic – Water hating

• Good Lubricants and metal preservers

• C1 to C4 = (Gas) Fuels - Methane

• C5 to C8 = (Liq.) Fuels - Gasoline

• C9 to C16 = (Viscous Liq.) – Diesel Fuel

• C17 and Up = (Very Viscous) - Greases

Cont.

http://web.mst.edu/~wlf/chem381/chap11.html

Hydrocarbons and Saturation

• Hydrocarbons are compounds that only contain Carbon and Hydrogen

• Alkanes are saturated hydrocarbons

– Carbons are saturated with hydrogen

• Compounds with double or triple bonds are unsaturated (more later)

Alkane Nomenclature

• Alkanes are named according to the longest carbon chain. (per IUPAC rules)

• System of prefixes to determine the number of carbons that are present.

1 = meth, 2 = eth, 3 = prop, 4 = but, 5 = pent

6 = hex, 7 = hept, 8 = oct, 9 = non, 10 = dec

• All alkanes end in -ane

• Example – Draw the structural, graphical, and skeletal formula for ethane and butane

• Example – Give the name and graphical formula for an alkane with 7 Carbons

Alkane Nomenclature

• Alkanes end in –ane

• Alkanes without branches are named according to the number of carbons

• Alkanes with branches are named according to longest chain of carbons

• The longest chain is numbered so that substituents receive the lowest number

Cont.

• When more than one of the same substituents is present use the prefixes di- tri-, tetra-

• If two or more substituents are present they are listed alphabetically (except prefix)

• Numbers are separated by commas, numbers and letters by hyphens

Substituent Groups

• Alkyl Groups – A hydrocarbon missing a hydrogen

CH3 – Methyl

CH3CH2 – Ethyl

CH3CH2CH2 – Propyl

CH3CH2CH2CH2 – Butyl • HalogensCl – Chloro Br – BromoF – Fluoro I – Iodo

• Name the alkane

• Name the alkane

• Name the alkane

• Name the alkane

• Name the alkane

• Name the alkane

• Name the alkane

Other Alkyl Groups

• Isopropyl

• Sec-Butyl

• Isobutyl

• Tert-butyl

• Name the alkane

• Name the alkane

• Name the alkane

• Name the alkane

Isomers

• Same formula different compound

• Structural Isomers

– Completely different bonding pattern

• Stereoisomers

– Same bond pattern

• Draw and name the isomers of C4H10

Homework

• Organic Worksheet #2

• Read pages 51-60

Dash Line Wedge Drawings

• A way of representing arragement in space

• Lines represent bonds in the plane

• Wedges come out of the plane and

• Dashed lines go into the plane

• Draw for Methane

Newman Projections

• Another way of showing arrangement in space.

• Look at the molecule for the end view

• Draw Newman Projection for Ethane

Alkane Confromations

• Alkanes are free to rotate because of single bond.

• Overlap of one orbital (sigma bond)

• Different arrangements are called rotamers.– A Stereoisomer

• Rotate to give minimum repulsion

• Draw the most stable conformation of chloropropane

Cycloalkanes

• Alkanes that from ring structures

• Not necessarily a circle

• All carbons are still sp3 hybridized

• Saturated compounds

• General Formula CnH2n

Cycloalkane Nomenclature

• Named by placing cyclo- in front of the alkane name of the longest carbon ring

• If there is only one substituent there is no need to number it

• If there are multiple substituents the must be numbered.– Number by alphabetical order

• Name the cycloalkane

• Name the cycloalkane

• Draw cyclopentane and cyclohexane

• Name the cycloalkane

• Name the cycloalkane

• Draw 1-chloro-4-ethyl-2-methylcyclohexane

Conformations of Cycloalkanes

• Cycloalkanes take on interesting shapes

• Consider cyclopropane

• What must the bond angles be?

• 60 degrees!– Because 3 points determine a plane

Cont.

• Consider cyclobutane

• What are the bond angles?

• 88 degrees

• There is a slight “puckering” of the bonds

Cont.

• Consider cyclohexane

• What must the bond angles be?

• 109.5!

• Six membered rings are very common

• Takes on two puckered conformations

• Chair and boat conformations

Chair Conformation

• Named because it looks like a chair

• Most stable conformation

Boat Conformation

• Less stable because of repulsion

Configurational Isomers

• Same bond pattern different arrangement in space

• Called cis- and trans- isomers

• Cis- same side Trans- opposite

• Cis and trans molecules are different molecules

• Different boiling points

• Fig. 2.7 in book. (Page 60)

• Draw the cis and trans forms of 2,3-dimethylcyclopropane

Homework

• Chapter 2 #’s 33,34,36,37ab,41

• Organic Worksheet #3

Reactions of Alkanes

• Alkanes are fairly boring from a chemistry point of view.

• Meaning they are fairly unreactive

• Make very good solvents

• Two types of reactions

– Burning

– Reacting with halogens

Combustion

• When alkanes react with oxygen they can burn

• Complete combustion of alkanes yields carbon dioxide and water

CH4 + 2O2 CO2 + 2H2O + heat

• Incomplete combustion yeilds carbon monoxide and water

Halogenation

• Process of adding a halogen to an alkane

• Process must take place in the light

• General form

R – H + X – X R –X + H – X

• Where R is an alkane and X is a halogen

• Called a substitution reaction

• A hydrogen is substituted for a halogen

• When chlorine is added it is called chlorination and so on

Cont.

• Excess halogen allows the reaction to continue

CH4 + 4 X2 CX4 + 4 HX

• Reactions of straight chain alkanes gives a mixture of products

C3H8 + Cl2 ?

Cycloalkanes

• Unsubstituted cycloalkanes give only one product when reacted with a halogen

• Write the balanced reaction when cyclobutane is reacted with bromine

Mechanism of Substitution

• The Mechanism is a process by which the reaction takes place

• Halogenation is a Free Radical Chain Reaction

• Made up of three steps– Initiation– Propagation– Termination

Initiation

• Beginning step

• Energy from light is required to break the halogen bond (Weaker than C-C or C-H)

• Creates a radical (Free atom)

Propagation

• Continuing the reaction

• Radicals react with the alkane and more halogens to create more radicals

Termination

• Ending the reaction

• Radicals react with radicals to stop the reaction

Problems

• 2.44