Organic Chemistry

The chemistry of compounds containing carbon.

Refinery and tank storage facilities, like this one in Texas, are needed to change the hydrocarbons of crude oil to many different petroleum products. The classes and properties of hydrocarbons form one topic of study in organic chemistry.

hydrocarbons

A hydrocarbon is a compound consisting of only hydrogen and carbon.

The carbon to carbon can be single, double, or triple bonds.

The bonds are always nonpolar.

HYDROCARBONS

Here are some Characteristics of hydrocarbons:

Has non-polar molecules

sp3 hybridization

Contains only hydrogen and carbon

non-electrolytes because of poor ionization

In "most** situations, it is not soluble in water

The reactivity is very slow

The low boiling point makes it pretty easy to decompose

an organic compound (as acetylene or butane) containing only carbon and hydrogen and often occurring in petroleum, natural gas, coal, and bitumens

Presented by Brent Daigle, Ph.D. (ABD)

Carbon-to-carbon bonds can be single (A), double (B), or triple (C). Note that in each example, each carbon atom has four dashes, which represent four bonding pairs of electrons, satisfying the octet rule.

Carbon-to-carbon chains can be (A) straight, (B) branched, or (C) in a closed ring. (Some carbon bonds are drawn longer, but are actually the same length.)

Straight vs branched

Classification of Organic Molecules

Functional Groups

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1. Hydrocarbons - molecules that possess only hydrogen and carbon

a1. Alkanes – noncyclic hydrocarbons with only C-C single bonds. Formula CnH2n+2 where n is an integer.

a2. Cycloalkanes – cyclic hydrocarbons with only C-C single bonds. Formula CnH2n where n is an integer.

Example: Butane CH3CH2CH2CH3 C4H10

Example: Cyclobutane C4H8

b1. Alkenes – noncyclic hydrocarbons with C=C double bonds. Formula CnH2n where n is an integer.

Example: 2-Butene CH3CH=CHCH3 C4H8

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c. Alkynes – noncyclic hydrocarbons with C≡C triple bonds. Formula CnH2n-2 where n is an integer.

Example: Butyne CH3C ≡ CCH3 C4H6

b2. Cycloalkenes – cyclic hydrocarbons with C=C double bonds. Formula CnH2n-2 where n is an integer.

Example: Cyclobutene C4H6

d. Aromatic Hydrocarbons – benzene and its derivatives

C

CC

C

CC H

H

HH

H

H

or C6H6

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2. Compounds containing Oxygen

a. Alcohols R-OH

Functional Group OH hydroxyl group

CH3OH methyl alcohol HOCH2CH2OH ethylene glycol (antifreeze)

b. Ethers R-O-R

CH3CH2-O-CH2CH3 Diethylether

c. Aldehydes and Ketones

R-C-H

O

R-C-R'

O

Functional Group C=O carbonyl group

OO

O

H

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d. Carboxylic Acids

Functional Group -CO2H -COOH -COH Carboxyl Group

R-C-OH

O

O

CH3-C-OH

O

OH2H3O+ CH3CO-

O

+ +Acetic Acid

e. Derivatives of Carboxylic Acids

R-C-OR'

O

R-C-Cl

O

R-C-NH2

O

Ester Acid Chloride Amide

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3. Nitrogen-Containing Molecules

a. Amines R-NH2

Functional Group -NH2 amino groupCH3NH2

NH

N

Amines are Lewis and Bronsted bases because of the nonbonded pair of electrons

NH2ClH NH3+ Cl+..

b. Amides (see above)

c. Nitriles R C N

Functional Group Cyano Group

C N

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Single versus Double Bonds

C C

H

H

HH

H

H

Ethane

The carbon-carbon single bond in ethane freely rotates at room temperature.

CC

HH

HH

Ethylene

The carbon-carbon double bond in ethylene does not freely rotate at room temperature.

Why not?

CC

HH

HH

C C

HH

H

HH

H

Answer: The Pi bond would have to be broken. It will not break at room temperature

Pi bond broken

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Isomers – different compounds with the same formula

a. Constitutional (Structural) Isomers – isomers that differ in their bonding sequence

CH3CHCH2CH3\

CH3

CH3CH2CH2CH2CH3vs

C5H12 C5H12

C=CCl

H H

Br

C=CH

H Cl

Br

C2H2BrCl C2H2BrCl

b. Stereoisomers – isomers that differ in their spatial orientation

C=CCl

H H

Br

C=CCl

H Br

H

C2H2BrCl C2H2BrCl Cis isomer Trans isomer

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Use of Wedges and Dashed Lines

CH

H

HH

Solid Wedge indicates “coming toward you”Dashed Line indicates “going away”Narrow Line indicates “in the plane of paper”

CH3

CH3

CH3

CH3

Question: Are the above cycloalkanes constitutional or stereoisomers?

Answer: Stereoisomers

ALKANE Alkanes are hydrocarbons with only single bonds.• SATURATED HYDROCARBONS – they contain only C

& H• they have only C-C and C-H single bonds• Contain the maximum possible number of H per C• Occasionally referred to as ALIPHATIC compounds;

Greek aleiphas, meaning fat (many animal fat contain long carbon chains similar to alkanes)

Alkanes occur in what is called a homologous series.

Each successive compound differs from the one before it only by a CH2

The AlkanesCharacteristics

AKA Paraffins, are chemical compounds that consist only of the elements carbon (C) and hydrogen (H). Each are linked by a single bond.

Each carbon atom must have 4 bonds (either C-H or C-C bonds), and each hydrogen atom must be joined to a carbon atom (H-C bonds).

General formula CnH2n+2 (Linear saturated hydrocarbon)

Brent Daigle, Ph.D. (ABD)

Methane

PHYSICAL PROPERTIES1. Non-polar –

comparable EN of C & H; symmetrical cmpd.

2. Low b.p. (-161.5o), or low m.p.(-83o) – weak VW attraction.

3. Colorless4. Sp. Gravity = 0.4 g/mL5. Slightly soluble in water

the simplest alkane

Chemical structure of methane

Tetrahedral109.5o

MW=16 g/ml

SOURCES:1. END PRODUCT OF ANAEROBIC

DECAY OF PLANT AND ANIMALS It is a major constituent of natural

gas (97%) Fire damp of coal mines Marsh gas bubbling in swamp Methane can be isolated by

fractional distillation

2. OXIDATION BY HALOGENS (HALOGENATION)

The Alkanes

Methane H

H C H CH4

H

Propane H H H

H C C C H C3H8

H H H

Ethane H H

H C C H C2H6

H H

Presented by Brent Daigle, Ph.D. (ABD)

Vocabulary Review (Time to pull out the ‘ole Latin Textbook)

The number of carbon atoms = root name! meth 1 carbon eth 2 carbon prop 3 carbon but 4 carbon pent 5 carbon hex 6 carbon hept 7 carbon oct 8 carbon non 9 carbon dec 10 carbon

Presented by Brent Daigle, Ph.D. (ABD)

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Physical Properties of Alkanes1. Combustion - Alkanes are flammable, i.e. they burn.

CH4 O2 CO2 OH2+ +2 2

2. Boiling and melting points a. Both bp and mp increase with increasing carbon number for straight-chain alkanes with formula CnH2n+2

Carbon Number Physical State C1- C4 gases C5 – C16 liquids C17 – C30 oils and greases C30 – C50 paraffin waxes >C50 plastics (polyethylene)

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b. Branching tends to lower the boiling point and raise the melting point

BP 60oC 58oC 50oC

MP -154oC -135oC -98oC

Explanation: MP Branching reduces the flexibility of the molecule which

reduces the entropy term S in the equation Tmp = H/S. Since S is in the denominator,

Tmp increases.

BP Branching reduces surface area (more compact structure), and therefore London dispersion forces which control boiling point for these molecules.

3. Solubility – alkanes are nonpolar molecules and therefore insoluble in water,which is polar. Alkanes are hydrophobic.

4. Densities – alkanes are less dense than water, with densities near 0.7 g/mL. Therefore they float on water, e.g. Exxon Valdez oil spill.

Petroleum is a mixture of alkanes, cycloalkanes, and aromatic hydrocarbons. Petroleum is formed from the slow

decomposition of buried marine life, primarily plankton and algae.

As petroleum is formed it is forced through porous rock until it reaches an impervious layer of rock. Here it forms an accumulation of petroleum

and saturated the porous rock creating an oil field.

Crude oil is the petroleum that is pumped directly from the ground. It is a complex mixture of

hydrocarbons with one or two carbon atoms up to a limit of about 50 carbon atoms.

This is usually not useful, so it must separated by distillation.

Crude oil from the ground is separated into usable groups of hydrocarbons at this Louisiana refinery. Each petroleum product has a boiling point range, or "cut," of distilled vapors that collect in condensing towers.

Petroleum products and the ranges of hydrocarbons in each product.

The octane rating scale is a description of how rapidly gasoline burns. It is based on (A) n-heptane, with an assigned octane number of 0, and (B) 2,2,4-trimethylpentane, with an assigned number of 100.

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Octane Number

Straight-chain hydrocarbons have low octane and make poor fuels.

Octane Number = 0

Branched Alkanes burn more slowly and reduce the knocking in the engine.

heptane

2,2,4-trimethylpentane

Octane Number = 100

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1. The first step in petroleum refining is fractional distillation.

Distilling Crude Oil

Separate fractions

based on differences in boiling point.

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Refining of Petroleum

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2. Upstream processing of the distillates.

a. Catalytic hydrocracking – produces small alkanes from large alkanes by adding hydrogen.

H2, heat

Si-Al catalyst

b. Catalytic cracking – produces small alkenes and alkanes by cracking in the absence of hydrogen.

heat

Si-Al catalyst

c. Catalytic Reforming – the alkanes and cycloalkanes are upgraded to higher octane number by conversion into aromatic compounds.

-3H2-H2

catalyst, heat catalyst, heat

Alkyl Groups Removing HYDROGEN from

an alkane, the partial structure that remains is called an ALKYL GROUP.

Are NOT stable compounds themselves, they are simply PARTS of larger compounds.

Are named by replacing the –ane ending of the parent alkane with a –yl ending.

In naming alkyl groups: the prefixes sec- (for secondary) and tert- (for tertiary) used for the C4 alkyl groups, refers to the number of other carbon atoms attached to the branching carbon atom.

There are 4 possibilities: primary (1o), secondary (2o), tertiary (3o) and quaternary (4o).

Sample problems

answers

NOMENCLATURE