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Organic Chemistry

February 18, 2014

What does “organic” mean?

• “Organic”

– Describes products

– Grown through “natural” biological process

– Without “synthetic” materials

• In the 18th century

– Produced by a living system

– Could not be produced in a lab

“Organic”

• In 1828– German chemist: Friedrich Wohler

– Reacted two inorganic compounds

– Obtained urea (organic compound)

Our Definition

• Organic Compound– A molecular compound containing carbon

• Not including (CO(g), CO2(g), HCN(g))

“Organic Chemistry”

• Organic Chemistry

– Is the study of compounds in which carbon is the principle element

– Example: animals, fossil fuels, plants

Carbon

• Atom can form four bonds– Four valence electrons

– Bond angle: 109.5o

• Atoms can bond together to form– Chains, Rings, Spheres, Sheets, Tubes

• Form combinations of bonds– Single, Double, and Triple bonds

• Carbon chains are the backbone of many molecules

Hydrocarbons• A compound containing only carbon and

hydrogen atoms

• There are two main classes: aliphatic and aromatic

Hydrocarbons

• Aliphatic hydrocarbons

– A compound that has chains or rings of carbon

• Does not include aromatics

• Aromatic hydrocarbons

– Compound based on a ring of six carbons

– Formula: C6H6

– All six bonds: intermediate between single and double bonds

Alkanes

• Saturated hydrocarbon– Only has single bonds between carbons

• General Formula

–CnH2n+2

First 10 AlkanesCH4 methaneC2H6 ethane C3H8 propane C4H10 butane C5H12 pentane C6H14 hexaneC7H16 heptaneC8H18 octaneC9H20 nonane

C10H22 decane

Prefix: based on the number of carbons in the longest chainSuffix: “ane” ending

Diagrams

• Expanded Structural Diagrams

– The normal structures of a few alkanes

methane propane

hexaneC

H

H

H

H C C C

H

H

H

H

H

H

H

H

C C C

H

H

H

H

H

H

H H

H

H

H

H

H

H

CCC

Building/Drawing Alkanes

• C2H6

• C3H8

• C5H12

Structural Isomers

• Structural Isomers

– Compounds with the same chemical formula

– Have the same molecular mass

– Different arrangements of atoms

– Physical and Chemical properties may be different

C C C

H

H

H

H

H

H

H

C C

H H

H

HH

C C C

H

H

H

H

H

H

C

H

H

C

HH H

H

Alkyl Groups• One (or more) carbon branches attached to

the main chain of the hydrocarbon

• Naming

– Drop the –ane of the corresponding alkane

– End with –yl

• General Formula: CnH2n-1

• Type of substituent group

– Anything that replaces hydrogen in an organic molecule

Alkyl Group

• Carbon chain added to the parent chain– methyl

– ethyl

– propyl

– butyl

– pentyl

– hexyl

• Follow the same prefixes as the parent chain

• End in “yl”

Naming Alkanes

1. Identify the longest continuous carbon chain– BE CAREFUL! It may not be in a straight line

Longest chain is 5 carbon atoms

2. Number the carbon atoms– Start with the end nearest to the substituent

group

CH2 CH2 CH CH3

CH3CH3

CH2 CH2 CH CH3

CH3CH3

1234

5

Naming Alkanes

3. Name the chain by adding “-ane”– pentane

4. Name the substituent group– Methyl

5. Attach the name of the group as a prefix

AND the attached carbon number– 2-methylpentane

CH2 CH2 CH CH3

CH3CH3

1234

5

Naming Alkanes

6. If two or more of the same group occur– Use prefixes: di, tri, tetra, etc.

– Locate their position on the main chain

– Separate numbers by commas

– Separate words by hyphens

2,3-dimethylpentane

CH2 CH CH CH3

CH3CH3

CH3

12345

Naming Alkanes

7. If different groups are present

– Arrange in alphabetical order

– Use numbers to indicate their position

5 - ethyl - 2,3,6 - trimethyloctane

CH3 CH CH CH2 CH CH CH2 CH3

CH3

CH3

CH2

CH3

CH31 8

Alkyl Halides

• An alkane in which one or more hydrogen atoms have been replaced by one or more halogen atoms

F- fluoro Cl- chloro Br- bromo I- iodo

• Other common groups

NO2- nitro NH2- amino

Naming Alkyl Halides

• Use the same rules as naming alkanes with branches

1-bromo-3,4-dimethylpentane

1,1,2-trichloro-3-methylpentane

4-ethyl-2-fluoroheptane

CH2 CH2 CH CH

CH3

CH3

CH3

Br

CH CH CH CH3

CH2 CH3

ClCl

Cl

CH3 C H

F

C H2 C H

C H2 C H 3

C H 2

C H 2

C H 3

Drawing Organic Molecules

• Expanded Structural Diagrams– Shows all bonds between atoms

• Condensed Structural Diagrams– Combine carbon atoms and the hydrogens bonded

• Line Diagrams– Only show carbon bonds

– Assumed hydrogens are attached appropriately

CH3CH2CH2CH2CH3

C C C

H

H

H

H

H

H

H

C C

H H

H

HH

Alkenes• Contain at least one carbon double bond

(C=C)

• Unsaturated

– Less than the maximum quantity of hydrogen

• More reactive than alkanes

• General Formula: CnH2n

Examples

– Ethene C2H4

– Propene C3H6

– Butene C4H8

1-butene 2-butene

C C

H

H

H

H

C C

HH

H CH3

C C

HH

H CH2CH3

C C

HH

CH3CH3

but-1-ene but-2-ene

Naming Alkenes

• General Rules for Naming

1. All alkane rules apply

2. Change the ending to “-ene”

– Must include double bond(s) in the chain

3. Start numbering carbons closest to double bond

Naming Alkenes

4. Include the number of the bonded carbon– Either in front of chain name or before suffix

5. More than one double bond– Use prefix before suffix

– di, tri, tetra, etc.

1, 3 pentdiene pent-1,3-diene

Geometric Isomers

• Carbon-carbon double bonds

– Not free to rotate (sigma + pi bonds)

• Two structures can exist

• Example: 2-butene

C C

HH

CH3CH3

C C

H

CH3

CH3

H

cis-2-butene trans-2-butene

Geometric Isomers

“cis”

– Latin for “on this side”

– C or “sis”

“trans”

– Latin “across”

– “trans”atlantic

cis-1,2-dichloroethene(mp = -81OC; bp = 60OC)

C C

H

Cl Cl

H

C C

H

H Cl

Cl

trans-1,2-dichloroethene(mp = -81OC; bp = 48OC)

Alkynes• Contain at least one carbon triple bond

• Unsaturated

– Less than the maximum quantity of hydrogen

• More reactive than alkanes (and alkenes)

• General Formula: CnH2n-2

Naming Alkynes

• General Rules for Naming

1. All alkane/alkene rules apply

2. Change the ending to “-yne”

– Must include triple bond(s) in the chain

3. Start numbering carbons closest to triple bond

Naming Alkynes

4. Include the number of the bonded carbon– Either in front of chain name or before suffix

5. More than one triple bond– Use prefix before suffix

– di, tri, tetra, etc.

2-butyne 4-chloro-1-butyne

but-2-yne 4-chlorobut-1-yne

CH3 C C CH3 CH2 CH2 C C H

Cl

Cyclic Aliphatics

• Carbon atoms can also be arranged in rings

• Named after the corresponding “open chain”

– Same rules apply for alkanes, alkenes, alkynes

• Prefix cyclo

• Substituents can be named after based on position

CH2

CH2 CH2

CH2CH

CH

CH2 CH2

CH2

cyclobutane cyclopentene 3-ethylcyclopentene

CH

CH

CH2 CH2

CH CH2 CH3

Cyclic Aliphatics

• For convenience, you can draw the corresponding polygon for each size of carbon ring

– Triangle (3 carbon), square (4 carbon), etc.

• It is understood that the appropriate number of hydrogens are attached

cyclopentene 1,2,3-trimethylcyclohexane

CH3

CH3

CH3

Structural Isomers• The number of structural isomers increase as

the number of carbon atoms increase

Properties of Hydrocarbons

Physical Properties of Hydrocarbons

• Since C and H have similar electronegativities, there are covalent bonds– Generally non-polar molecules

• The main intermolecular force is van der Waals forces. These are weak, making the compound easy to separate.

• Van der Waals forces: the attraction of electrons of one molecule for the the nuclei of another molecule

• As the compound gets larger in size, the strength of VDW forces increases, leading to higher MP and BP

Fractional Distillation

Reactions of Hydrocarbons

Reactions of Alkanes

• ALL hydrocarbons undergo COMBUSTION REACTIONS, making them useful fuels

• Complete Combustion: chemical reaction that involves a compound reacting with O2 to produce carbon dioxide, water and thermal energy

Reactions of Alkanes

• Alkanes are generally unreactive

– Single C-C bonds are hard to break

• Primarily undergo SUBSTITUTION REACTIONS

– Reaction that replaces a hydrogen atom with another atom or group of atoms

Reactions of Alkanes

• H can be substituted by a halogen atom

– Halides (Br2) or Hydrogen halides (HBr)

– Form ALKYL HALIDES

• Usually requires heat or UV light

– Reactions involving F2 are vigorous

Reactions of Alkanes

• As the reaction proceeds:

• Additional bromines can be added resulting in a mixture of brominated products

– Separated by fractional distillation

Reactions of Alkenes and Alkynes

• Due to the presence of multiple bonds– Alkenes/Alkynes are MORE REACTIVE than

alkanes

• For example, reactions with Br2 are vigorous at room temperature– Alkanes require heat or UV light to react

• Undergo ADDITION REACTIONS– Atoms are added to the compound without loss of

hydrogen

• There are FOUR types of ADDITION reactions

• Classified by the type of compound being reacted

1. Halogenation – reaction with halogen

Reactions of Alkenes and Alkynes

2. Hydrogenation – reaction with H2

Reactions of Alkenes and Alkynes

3. Hydrohalogenation – reaction with hydrogen halides (HX)

Reactions of Alkenes and Alkynes

4. Hydration – reaction with water

Reactions of Alkenes and Alkynes

Markovnikov’s Rule

• When a hydrogen halide or water molecule reacts with an Alkene,

– the hydrogen atom will generally bond to the carbon atom in the multiple bond that has the most hydrogen atoms already bonded to it

Aromatic Hydrocarbons

• Aromatic hydrocarbons are benzene or a compound that contains a benzene ring

• Benzene has the formula: C6H6

CH5

CH4

CH6

CH3

CH1

CH2

Aromatic Hydrocarbons

• Electrons involved in the double bonds are equally shared among the 6 carbons

• Benzene can be thought of as a hybrid of two “resonance forms”

• A common way to represent benzene

Aromatic Hydrocarbons

General Rules for Naming

• The benzene ring is usually considered the parent chain

1. If an alkyl group is attached to benzene, the compound is named alkylbenzene

Cl

Br

F

NO2

fluorobenzene chlorobenzene

bromobenzene nitrobenzene

Aromatic Hydrocarbons

2. If more than one alkyl group is attached to the benzene ring, number each using the lowest combination of numbers (IUPAC)

Cl

Cl

Cl

Cl

1,2-dichlorobenzene 1,3-dichlorobenzene

1 1

22

3

4

5 5

4

66

3

Aromatic Hydrocarbons

• Occasionally, benzene groups are found as a substituent to more complex hydrocarbon chains.

• The benzene is called phenyl

3-chloro-2-methyl-4-phenyl-2-pentene

C C CH CH3

CH3

CH3 Cl

Ortho, Meta, Para

• Alternate system using relative position

Example: diethylbenzene

o-diethylbenzene m-diethylbenzene p-diethylbenzene

o = ortho m = meta p = para

Practice

Properties of Aromatics

• Most are liquids at room temperature

– Some are crystalline solids

• Symmetrical structures

– Non-polar (unless it has an electronegative substituent)

– Generally insoluble in water

Reactions of Aromatic Compounds

• Unique bonding makes the bond strength greater than alkenes

• Much less reactive than alkenes

• Undergoes SUBSTITUTION Reactions

– Like alkanes

Reactions of Aromatic Compounds

• Further reactions with halogens (Br2) can result in additional substitutions. In theory, the bromine can replace any hydrogen.

Substitution Reactions with Benzene

Difference with 6 carbon rings