Chapter 22 Hydrocarbon Compounds

Organic Chemistry and Hydrocarbons

Organic originally meant chemicals that came from organisms

1828 German chemist Friedrich Wohler synthesized urea in the lab

Today, organic chemistry is the chemistry of virtually all compounds containing the element carbon

Organic Chemistry and Hydrocarbons

Over a million organic compounds, with a dazzling array of properties

Why so many? Carbon’s unique bonding ability!

Let’s start with the simplest of the organic compounds: Hydrocarbons

Organic Chemistry and Hydrocarbons

Hydrocarbons contain only two elements: hydrogen and carbon– simplest hydrocarbons called

alkanes, which contain only single covalent bonds

– methane (CH4) with one carbon is the simplest alkane. It is the major component of natural gas

Models of Methane

Organic Chemistry and Hydrocarbons

Review structural formula- p. 698 Carbon has 4 valence electrons,

thus forms 4 covalent bonds– not only with other elements, but also

forms bonds WITH ITSELF.

Ethane (C2H6) is the simplest alkane with a carbon to carbon bond

Straight-Chain Alkanes

Straight-chain alkanes contain any number of carbon atoms, one after the other, in a chain -meaning one linked to the nextC-C-C C-C-C-C etc.

Names of alkanes will always end with -ane

Straight-Chain Alkanes

Combined with the -ane ending is a prefix for the number of carbons– Table 22.1, page 700

Homologous series- a group of compounds that have a constant increment of change

In alkanes, it is: -CH2-

Alkane Hydrocarbons

Alkane Prefixes – The root indicates the

number of carbon atoms

Name Molecular Form

Methane CH4

Ethane C2H6

Propane C3H8

Butane C4H10

Pentane C5H12

Hexane C6H14

Heptane C7H16

Octane C8H18

Nonane C9H20

Decane C10H22

Straight-Chain Alkanes Many alkanes used for fuels:

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 Condensed structural formulas?

Note examples on page 702

Alkane Melting and Boiling Points

Functional Groups

Most organic chemistry involves replacing one or more of the hydrogen atoms with a ‘substituent group’– Groups often contain C, O, N, S, or P– They are also called “functional groups”-

the chemically functional part of the molecule. They change the properties or function of the molecule.

AlcoholsAlcohols - a class of organic

compounds with an -OH group–The -OH functional group in

alcohols is called a “hydroxyl” group; thus R-OH is the formula

How is this different from the hydroxide ion with basics? (covalent bonding with carbon- not ionic with a metal such as sodium)

Methanol Structure

Ethanol Ball and Stick

Alcohols Both IUPAC and common names For IUPAC:

–drop the -e ending of the parent alkane name; add ending of -ol, number the position of -OH

–parent is the longest chain that contains the carbon with the hydroxyl attached.

AlcoholsCommon names:

–similar to halocarbons, meaning name the alkyl group followed by the word ‘alcohol’

–One carbon alcohol = methyl alcohol

Properties of Alcohols Denatured alcohol- means it has

been made poisonous by the addition of other chemicals, often methyl alcohol (methanol, or wood alcohol). As little as 10 mL of methanol has been known to cause permanent blindness, and 30 mL has resulted in death!!!

Alkenes Multiple bonds can also exist

between the carbon atoms Hydrocarbons containing carbon to

carbon double bonds are called alkenes C=C C-C=C

Called “unsaturated” hydrocarbons if they contain double or triple bonds

Alkynes Hydrocarbons containing carbon to

carbon triple bonds called alkynes

-C C- Alkynes are not plentiful in nature Simplest is ethyne- common name

acetylene (fuel for torches) Table 22.5, page 715 for b.p. and m.p.

Section 22.5Hydrocarbons from the Earth

OBJECTIVES:

–Identify three important fossil fuels and describe their origins.

Natural Gas

Fossil fuels provide much of the world’s energy

Natural gas and petroleum contain mostly aliphatic (straight-chain) hydrocarbons

Natural gas is an important source of alkanes of low molecular mass

Natural Gas

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

propane, and 2% butane with the remainder being nitrogen and higher molar mass hydrocarbons

– also contains a small amount of He, that is recovered and used in various industries, including balloons

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

Insufficient burning has a yellow flame, due to glowing carbon parts, as well as making carbon monoxide

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

Petroleum Fractional Distillation

Crude Oil Components

Petroleum It is separated by distillation into

fractions, according to boiling pt. Fractions containing higher molar

mass can be “cracked” into more useful shorter chain components, such as gasoline and kerosene– involves catalyst and heat– starter materials for plastics and

paints

Petroleum Cracking

Coal From huge fern trees and mosses

decaying millions of years ago under great pressure

Stages in coal formation:

1. Peat- soft, fibrous material much like decayed garden refuse; high water content. After drying will make a low-cost, smoky fuel

Coal2. Lignite- peat left in the ground

longer, loses it’s 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 after more time; lower water content, higher C content (70-80%)

Coal4. Anthracite, or hard coal

– carbon content exceeding 80%, making it an excellent fuel source

Coal may be found close to the surface (strip-mined), or deep within the earth

Pollutants from coal are common; soot and sulfur problems

Scrubbing Sulfur From Coal

Coal Coal may be distilled for many

products– coal gas, coal tar, coke, and ammonia

– further distilled into benzene, toluene, naphthalene, phenol, and pitch

– Coke is almost pure carbon; produces intense heat and little or no smoke, thus used in industrial processes