Tips for Organic Chemistry Success

Chapter 12 – Saturated Hydrocarbons
Organic vs. Inorganic Compounds
•Inorganic compounds: cpds which are NOT hydrocarbons (~1.5 million)
•Organic compounds: cpds which contain hydrogen & carbon (thus,
hydrocarbons & derivatives) (~ 7 million)
•“Organic Chemistry” started, as a branch of chemistry, when F. Wohler
disproved the idea of “vital force.”
Carbon Atoms
Carbon atoms generally form 4 bonds (think about their electron configuration)
•In “organic” compounds these bonds are COVALENT.
•Carbon readily forms bonds with other carbon atoms as well as with atoms of
other elements.
Hydrocarbons & their Derivatives
•Hydrocarbons: H & C atoms only
•Derivatives: H, C & other elements
•Saturated Hydrocarbons: all C-C bonds are “single.”
•Unsaturated Hydrocarbons: one or more C-C bond(s) is/are multiple.
Alkanes: Acyclic Saturated Hydrocarbons (chains)
•General Formula: CnH2n+2
–Structural: (ex.: C4H10)
Alkane Nomenclature
Alkane Isomerism
Isomers: compounds that share the same molecular formula but have different
structural formulas
–With an increased number of C atoms, there is an exponentially increased
number of isomers
•Constitutional - same molecular formula, different structural formula;
differ in connectivity of atoms
–Ex. C4H10
butane ; isobutane
Alkyl Groups & IUPAC names
Use the following rules to properly name hydrocarbon molecules:
–1. Identify the longest, continuous chain of C atoms and name it.
–2. # the C atoms in the chain from the end nearest an alkyl group.
–3. # and name the attached alkyl group(s).
–4. If more than one alkyl group:
•first substituent must have lower number.
•Alkyl groups are listed in alphabetical order.
•Use prefixes when more than one identical substituent exists.
–5. Separate #s from each other with commas; separate names from
numbers with hyphens; do not use a hyphen/space after the last
substituent, before the parent alkane name.
Carbons are classified 4 ways in a chain:
–Primary, secondary, tertiary, quaternary
Branched-chain Alkyl Groups
“Simple”: 4 important ones to know!
Isopropyl, isobutyl, sec-butyl, tert-butyl
Complex: “select the longest chain as the “base” alkyl, add “substituents.”
Isomerism of Cycloalkanes
•Constitutional (ex.: C5H10) 5 isomers
•Stereoisomers: possible with substituted cycloalkanes
(ex.: 1,3-Dimethylcyclohexane)
–Cis- (SAME side)
–Trans- (ACROSS from)
Sources of Saturated Hydrocarbons
Natural Gas:
–Methane (50-90%); Ethane (1-10%); Propane & Butane (up to 8%)
Petroleum (crude oil): this is a complex mixture of both cyclic and acyclic
hydrocarbons which can be separated by a process known as fractional
Physical Properties of Hydrocarbons
All are insoluble in water
–Consider the polarity of the compounds, therefore they can make good
protective coatings
All are less dense than water (0.6-0.8 g/mL)
–Oil & water
Boiling Points & States of Matter
–Generally, BP increases with increasing # C atoms
•Reason: increasing LDF
–1-4 C atoms = gas; 5-17 C atoms = liquid; >17 C atoms = solid
–Isomers: Branched BP < Unbranched BP
–Cyclic Compounds have higher BP than Acyclic.
Chemical Properties of Hydrocarbons
Alkanes are the least reactive organic compounds. However, two major reactions
are common:
–R (some hydrocarbon) + O2 → CO2 + H2O + energy
–very exothermic reaction.
–If the quantity of O2 is insufficient, it will form a poison called
carbon monoxide (CO).
–Here is an example with methane:
CH4 + 2 O2 → CO2 + 2 H2O
with less O2:
2 CH4 + 3 O2 → 2 CO + 4 H2O (poison!)
with even less O2:
CH4 + O2 → C + 2 H2O (black soot forms)
–R-H + X2 --> R-X + H-X
Hydrocarbon fuels: Fossil fuels (solid, liquid, or gas) form from organic material
being covered by successive layers of sediment over millions of years
•Oil & natural gas: slow decomposition & burying of marine phytoplankton &
zooplankton that sank to the sea floor.
•Coal: ancient swamps and bogs - slow decomposition of land plants in anaerobic
–e.g. peat bogs of Ireland
Petroleum, Naphtha, or crude oil
From Greek petra = rock and oleum = oil
Thick, dark brown or greenish liquid
•Complex mixture of various hydrocarbons, largely of the alkane series
•May vary much in appearance, composition, and purity
•Petroleum is also the raw material for many chemical products: fuels &
•Can be altered into: fertilizers, pesticides, and plastics
•Think of the impact of a substantial oil crisis on our economy & society!
The complex hydrocarbon mixture present in petroleum is separated into simpler
mixtures by means of a fractionating column.
Natural gas
Natural gas mainly methane (does contain other “small” HC cpds).
•Highly flammable
•No ash and very little air pollution.
•From light portion of petroleum
•Rises thru fissures in earth’s crust
•Man-made wells can tap it
•Discovered thousands of years ago could be burned for heat and light.
•Colorless, odorless, & lighter than air.
•Mercaptan, chemical odorant, is added for gas leaks.
•natural gas combustion  CO2 + H2O
•Natural gas found in different underground formations: shale, sandstone beds,
coal seams, & deep, salt water aquifers
Problems associated with alkane hydrocarbons
•Hydrocarbon pollution: (oil spills) of aquatic environments (e.g. Exxon
•Global warming: CO2 and H2O
•Acid rain due to sulfur impurities in oil and coal: damage crops, lakes, buildings, etc.
•Smog and soot: increase respiratory problems
•Land fill: non-decomposing plastics
•Ozone depletion / increased UV radiation
Global warming: The Greenhouse effect:
Alkane substitution reaction: Incoming atom or group of atoms (orange sphere)
replaces a hydrogen atom in the alkane model.
–Treat halogen atoms like alkyl groups.
–F = fluoro; Cl = chloro; Br = bromo; I = iodo
Halogenation Reactions
General formula: RH + X2 → RX + HX
Hydrocarbon + Halogen  Halogenated + acid
(diatomic) hydrocarbon
CH4 + Cl2 -->
CH3Cl + HCl
Highly exothermic reaction: can lead to an explosion
Chlorofluorocarbons (CFCs)
Developed in the 1930's
Very stable compounds composed of C, F, Cl, & H
Freon tradename:
The Ozone Layer Chemistry
CFCl3 + UV Light ==> CFCl2 + Cl
Cl + O3 ==> ClO + O2
ClO + O ==> Cl + O2
The chlorine free radical atom
is then able to attack another
ozone molecule
Cl + O3 ==> ClO + O2
ClO + O ==> Cl + O2
and again ...
Cl + O3 ==> ClO + O2
ClO + O ==> Cl + O2
and again... thousands of times!
A catalyst!
The ozone destruction process requires conditions cold enough (-80oC) for stratospheric
clouds to form. Once these stratospheric clouds form the process can take place, even in
warmer conditions
Ozone consumption has been greatly reduced,
Saturated Hydrocarbons: What do you need to know?
–Structural characteristics (know the functional group)
–Nomenclature (the rules for naming the molecules)
–Physical and Chemical properties (basic/simple)
–Occurrence and
uses (common)
(what basic reactions produce the molecules)
–Characteristic reactions
of the molecules