Hydrocarbon Compounds - By Razi

7/29/2019 Hydrocarbon Compounds - By Razi

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(C4H10)


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Hydrocarbons

OBJECTIVES:

Describe the relationshipbetween number of valence

electrons and bonding incarbon.


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Hydrocarbons

OBJECTIVES:

Define and describe alkanes.


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Hydrocarbons

OBJECTIVES:

Relate thepolarity ofhydrocarbons to their

solubility.


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Organic Chemistry and

Hydrocarbons

Organic originally referred to anychemicals that came from organisms

1828 - German chemist FriedrichWohler synthesized urea in a lab

Today, organic chemistry is the

chemistry of virtually all compoundscontaining the element carbon


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Friedrich Wohler

1800 1882

Used inorganic

substances tosynthesize urea, a

carbon compound

found in urine.This re-defined

organic chemistry.


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Hydrocarbons Over a million organic compounds,

with a dazzling array of properties

Why so many? Carbons uniquebonding ability!

Lets start with the simplest of the

organic compounds. These are theHydrocarbons


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Hydrocarbons

Hydrocarbons contain only two

elements: 1) hydrogen, and 2) carbon

simplest hydrocarbons called alkanes,which contain only carbon to carbon singlecovalent bonds (CnH2n+2)

methane (CH4) with one carbon is thesimplest alkane. It is the major component

of natural gas


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Hydrocarbons

Review structural formulas - p.694

Carbon has 4 valence electrons, thus

forms 4 covalent bonds

not only with other elements, but also

forms bonds WITH ITSELF (nonpolar) Ethane (C2H6) is the simplest alkane

with a carbon to carbon bond


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Straight-Chain Alkanes

Straight-chain alkanes contain anynumber of carbon atoms, one afterthe other, in a chain pattern -

meaning one linked to the next (notalways straight)

C-C-C C-C-C-C etc.

Names of alkanes always will always

end with -ane


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Combined with the -ane ending is aprefix for the number of carbons

Table 22.1, page 695 Homologous series- a group of

compounds that have a constant

increment of change In alkanes, it is: -CH2- (methylene)


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Many alkanes used forfuels: methane,propane, butane, octane

As the number of carbons increases, so

does the boiling and melting pt.

The first 4 are gases; #5-15 are liquids;

higher alkanes are solids Condensedstructural formulas? Note

examples on page 696


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Naming Straight-Chain Alkanes

Names recommended by IUPAC - the

International Union ofPure and Applied

Chemistry

end withane; the root part of the name

indicates the # of carbons

We sometimes still rely on common

names, some of which are well-known


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Naming Straight-Chain Alkanes

IUPAC names may be long andcumbersome

Common names may be easier ormore familiar, but usually do notdescribe the chemical structure!

Methane is natural gas or swampgas


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Branched-Chain Alkanes

Branched-chain means that otherelements besides hydrogen may beattached to the carbon

halogens, oxygen, nitrogen, sulfur,and even other carbons

any atom that takes the place of a

hydrogen on a parent hydrocarbon iscalled asubstituent, or the branched

part


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A hydrocarbon substituent is called analkyl group or sometimes radicals

use the same prefixes to indicate the

number of carbons, but -ane ending isnow -yl such as: methyl, ethyl,

propyl, etc.

Gives much more variety to the organiccompounds


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Rules for naminggo from right toleft - page 698

1. Longest C-C chain is parent

2. Number so branches have lowest #

3. Give position number to branch

4. Prefix (di, tri) more than one branch5. Alphabetize branches (not prefix)

6. Use proper punctuation ( - and , )


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- Page 699


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From the name, draw the structure, in

a right-to-left manner:

1. Find the parent, with the -ane2. Number carbons on parent

3. Identify substituent groups (givelowest number); attach

4. Add remaining hydrogens


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- Page 700


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Section 22.2

Unsaturated Hydrocarbons OBJECTIVES:

Describe the differencebetween unsaturated andsaturated hydrocarbons.


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Section 22.2

Unsaturated Hydrocarbons OBJECTIVES:

Distinguish the structures ofalkenes and alkynes.


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Alkenes

Multiple bonds can also existbetween the carbon atoms

Hydrocarbons containing carbon to

carbon double bonds are calledalkenes(CnH2n) C=C C-C=C

Called unsaturated if theycontain double or triple bonds


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Naming Alkenes

Find longest parent that has the double

bond in it

New ending: -ene

Number the chain, so that the double

bond gets the lower number

Name and number the substituents

Samples on page 702


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Alkynes

Hydrocarbons containing carbon tocarbon triple bonds are calledalkynes

(CnH2n-2) -C C- Alkynes are not plentiful in nature

Simplest is ethyne- common nameacetylene (fuel for torches)

Table 22.3, p. 703 for boiling pt.

ethyne


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Section 22.3

Isomers OBJECTIVES:

Explain why structuralisomers have different

properties.


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Section 22.3

Isomers OBJECTIVES:

Identify optical isomers.


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Structural Isomers

Compounds that have the samemolecular formula, but differentmolecular structures, are calledstructural isomers

Butane and 2-methylpropane (made bybreaking carbon off the end, andmaking it a branch in the middle)

Also have different properties, such asb.p., m.p., and reactivity


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Structural Isomers of Butane, C4H10


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Stereoisomers

Dont forget that these structures are

really 3-dimensional

stereoisomers- molecules of the samemolecular structure that differ only in

the arrangement of the atoms in space.

Two types are a) geometric and b)

optical


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Geometric Isomers

There is a lack of rotation around a

carbon to carbon multiple bond

has an important structural implication Two possible arrangements:

1.trans configuration - substituted

groups on opposite sides of doublebond

2. cisconfiguration - same side


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Substituted

groups are on

opposite sidesof the double

bond (in this

case, one is

above, the other

is below)

Substituted

groups are on

the same sideof the double

bond (in this

case, both are

above)

Geometric Isomers

Trans-2-butene

Cis-2-butene


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Geometric Isomers

Trans-2-butene and Cis-2-butene shown

on page 705

differ in the geometry of the substitutedgroups (to double bond)

like other structural isomers, have

different physical and chemical properties( note page 705-middle)


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Optical Isomers

Asymmetric carbon? C with 4

different groups attached. Conceptual

Problem 22.4, p.706 Molecules containing asymmetric

carbons have handedness, and exist

as stereoisomers.

Figure 22.9, page 705


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Optical Isomers, and these will each show an

asymetric carbon (4 different branches attached)

The asymetric carbon


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Section 22.4

Hydrocarbon Rings OBJECTIVES:

Describe bonding in benzene.


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Cyclic Hydrocarbons

The two ends of the carbon chain are

attached in a ringin a cyclic

hydrocarbon sample drawings on page 709

named as cyclo-____

hydrocarbon compounds that do NOTcontain rings are known as aliphaticcompounds


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Aromatic Hydrocarbons

A special group of unsaturated cyclic

hydrocarbons is known as arenes

contain single rings, or groups of rings also called aromatic hydrocarbons, because

of pleasant odor

simplest aromatic is benzene (C6H6) Term aromatic applies to materials with

bonding like that of benzene


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Benzene is a six-carbon ring, withalternating double and single

bonds

exhibits resonance, due to location of

the double and single bonds-p.710

Benzene derivatives possible:

methylbenzene, 3-phenylhexane,

ethylbenzene (top page 711)


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Aromatic Hydrocarbons One derivative of Benzene is

called phenylethene, or commonlynamed STYRENE.

Foamed styrene is trademarked byDow Chemical as styrofoam

Other manufacturers items usuallyjust called foam cups

CHCH2


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Benzene derivatives can have two or

more substitutents:

1,2-dimethylbenzene

1,3-dimethylbenzene

1,4-dimethylbenzene

Can use ortho for 1,2; meta for 1,3; and

para for 1,4 (page 711)

C

C

CC


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Section 22.5

Hydrocarbons From EarthsCrust

OBJECTIVES:

Identify three important fossilfuels and describe their

origins.


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Section 22.5


OBJECTIVES:

Describe the composition ofnatural gas, petroleum, andcoal.


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Section 22.5


OBJECTIVES:

Describe what happens whenpetroleum is refined.


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Natural Gas

Fossil fuels provide much of the worldsenergy

Natural gas and petroleum contain mostly

the aliphatic (or straight-chain)hydrocarbonsformed from marine life

buried in sediment of the oceans

Natural gas is an important source of

alkanes of low molecular mass


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Natural Gas

Natural gas is typically:80% methane, 10% ethane, 4%

propane, and 2% butane with the

remainder being nitrogen and highermolar mass hydrocarbons

also contains a small amount of He,

and is one of its major sources


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Natural Gas

Natural gas is prized for combustion,

because with adequate oxygen, it burns

with a hot, clean blue flame:

CH4 + 2O2 CO2 + 2H2O + heat

Incomplete burning has a yellow

flame, due to glowing carbon parts, aswell as making carbon monoxide


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Petroleum

The compounds found in petroleum (or

crude oil) are more complex than those

in natural gas

Usually straight-chain and branched-

chain alkanes, with some aromatic

compounds also Crude oil must be refined (separated)

before being used


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Petroleum

It is separated by distillation into

fractions, according to boiling pt.

Fractions containing higher molar masscan be cracked into more useful

shorter chain components, such as

gasoline and kerosene involves catalyst and heat

starts materials for plastics and paints


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Coal

From huge fern trees and mosses

decaying millions of years ago under

great pressure of rocks / soil.

Stages in coal formation:

1. Peat- soft, fibrous material much like

decayed garden refuse; high watercontent. After drying will make a low-

cost, smoky fuel


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Coal

2. Lignite- peat left in the ground longer,

loses its fibrous texture, and is also

called brown coal

harder than peat; higher C content (50%);

still has high water content

3. Bituminous, or soft coal- formed aftermore time; lower water content, higher

C content (70-80%)


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Coal

Coal may be distilled for many products coal gas, coal tar, coke, and ammonia

further distilled into benzene, toluene,

naphthalene, phenol- the aromatics Coke is almost pure carbon; produces

intense heat and little or no smoke, thus

used in industrial processes


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Hydrocarbon Compounds - By Razi