organic part 2 - chemistry...

Mary J. Bojan Chem 110

Organic Part 2 Hydrocarbons

1. Alkanes: all single bonds 2. Alkenes: C=C

saturated v. unsaturated structural isomers geometric isomers

3. Alkynes: C≡C 4. Aromatic hydrocarbons

Reactivity of hydrocarbons •  addition reactions •  combustion reactions

Petroleum

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Hydrocarbons

This is the structure of 4-ethyl-2,3,3-trimethylnonane

What is the molecular formula of this compound?

How many ⎯CH3 groups are there on this compound?

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HYDROCARBONS Simplest organic compounds

Contain only C and H

Alkanes saturated have the maximum number of H attached to the C skeleton.

Alkenes unsaturated Alkynes have double or Aromatic triple bonds

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ALKENES Contain one or more double bonds

The C=C⎯H or C=C⎯C angle is 120°

CnH2n

Rotation about double bond is restricted

propene ethene (ethylene)

C C

CH

H

H

HC

4

CH

H

H

CH3

C


Butene C4H8 There are several possible structures for a chain of 4 carbons with one double bond.

1-butene 2-methylpropene

2-butene

cis-2-butene trans-2-butene 5


Structural isomers: same molecular formula: different structure

1-butene 2-methylpropene 2-butene

Structural vs. Geometric

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Geometric isomers same molecular formula: different geometry

cis-2-butene trans-2-butene

cis-isomer: same side trans-isomer: opposite side (across)


ALKYNES: CnH2n-2 Contain ⎯C≡C⎯

H⎯C≡C⎯H CH3⎯C≡C⎯H ethyne propyne

(acetylene) bond angle is 180°

structural isomers no geometric isomers are possible

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C C HC

H

H

C

H

H

H

C C CC

H

H

H

H

H

H

1-butyne 2-butyne


Reactions of Alkenes and Alkynes Addition reaction

–  Double and triple bonds are reactive: addition reactions typically occur at room temperature.

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For Alkenes CH3⎯CH=CH2 + Br2 →

or CH3⎯CH=CH⎯CH3 + HX →

where X = Cl, Br, I, OH, etc.

For Alkynes

CH3 ⎯C≡CH + 2Br2 →

CH3-C ≡C -CH3 + 2HCl →


Aromatic Hydrocarbons Contain alternating single and double C-C Bonds

Benzene is prototypical molecule

Usually written:

Aromatic hydrocarbons are less reactive than alkenes:

Special kind of bonding Have “delocalized” π electrons Results in added stability

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CCC

CCC

HH

HH

H

H CCCCCC

HH

HH

H

H


Reactivity of Hydrocarbons Same reaction: hydrocarbon + Br2

Colorless red

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CH3

ALKANE Heptane + Br2 ⎯→

ALKENE (and ALKYNES)

2-pentene + Br2 ⎯→

AROMATIC

toluene + Br2 ⎯→


Functional Group classes Contain a representative group of elements in a fixed pattern

Have similarities in structure and function (reactivity).

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Seemingly small changes in structure can have big affect on molecular properties

Functional Group Type hydrocarbon alcohol ether CH3⎯CH2⎯H CH3⎯CH2⎯O H CH3⎯O⎯CH3

ethane ethanol di-methyl ethe r g a s liquid g a s

bp –89°C bp 78°C bp –24 °C water soluble

Example: adding an oxygen changes a hydrocarbon into an alcohol or an ether…


Functional Group Classes Contain a representative group of elements in a fixed pattern:

Each class has similarities in structure and function (reactivity).

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Groups which have

a carbonyl

Aldehydes Ketones (R,R’≠H)

Alcohols R-OH R≠H

R = alkyl group

Ethers R-O-R’ R,R’≠H

Amines

N HHR

N R'HR

N R'RR"

CO

RC

H

O

R'C

R

O

Carboxylic Ester Amide Acid

OHC

R

O

OR'C

R

O

NHR'C

R

O


Functional Groups with O and N

Alcohols R⎯OH hydroxyl group

hydrocarbon (alkyl) group

Ether R⎯O⎯R’

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N HHR

N R'HR

N R'RR"

Amines


Functional Groups Containing the carbonyl group

Aldehyde

Ketone

Carboxylic Acids ⎯COOH

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C O

RC

H

O

R'C

R

O

OHC

R

O


Organic Acids and Bases

AMINES weak bases, organic bases (like NH3)

(CH3)3N(aq) + H+(aq) (CH3)3NH+(aq)

CARBOXYLIC ACIDS weak acids, organic acids

(aq) (aq) + H+(aq)

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HOC

RO

-OC

RO


Questions Which of the following hydrocarbon classes does NOT have a double or triple bond?

1 alkane 2 alkene 3 alkyne 4 aromatic

Which one of the following functional group classes does not have a double bond?

1 aldehyde 2   Ketone 3   amine 5   ester

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The presence and properties of functional groups are responsible for the action of drugs.

What functional groups are present in these molecules?

Acetyl salicylic acid Acetaminophen

Ibuprofen

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C

O

O C

O

OH

CH3

HO N

H

C

O

CH3

CH3

O

OH

H3C

CH3


What’s Next?

•  Formulas tell us how atoms are connected to each other

•  Lewis structures tell us where the electrons are.

QUESTIONS •  What are the shapes of these molecules? •  Can we use information about bonding,

connectivity of atoms, molecular formulas, etc. to predict the shapes (and properties) of molecules?

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organic part 2 - chemistry...

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