Chapter 10--Alkanes - College of Southern Maryland

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CHAPTER 10--ALKANES
Dr. Ellen Wilson, RPh, PhD
CHE1230
WHY ARE THERE SO MANY
ORGANIC COMPOUNDS?
WHY ARE THERE SO MANY CARBON COMPOUNDS?
Carbon
forms
stable,
covalent
bonds
with
other
carbon
atoms
What
does this
mean?
TYPES OF BONDING
Covalent Bonding
Ionic Bonding
Sharing of electrons
Transfer of electrons
CH3CH2CH2CH2CH3
Na+ + Cl- = NaCl
Organic chemistry bonding
Inorganic chemistry bonding
Partial charges & dipole
moments
Full charges, ions
Discrete molecules
Dissolve but don’t dissociate
Nonelectrolytes
Lattice structures
Dissociate in water
Electrolytes
WHY ARE THERE SO MANY
ORGANIC COMPOUNDS?
Carbon forms stable, covalent bonds with other
atoms such as H, O, N, S, and halogens
WHAT IS A FUNCTIONAL GROUP?
A specific group of atoms within a molecule that
help
define the properties and reactivity of the molecule
Will have the same properties regardless of the
molecule to which it is attached
COMMON FUNCTIONAL GROUPS
See inside back cover of text for these examples and more….
FUNCTIONAL GROUPS MAKE A BIG
DIFFERENCE
Butane
Pentane
Butanol
Gas
Liquid
Liquid
BP=-0.5oC
36.1oC
117.73oC
Insoluble in water
Soluble
FUNCTIONAL GROUPS GIVE UNIQUE PROPERTIES

Many biologically active molecules are esters,
ethers, carboxylic acids, and amines
FUNCTIONAL GROUPS ALLOW US TO
PREDICT PROPERTIES OF MOLECULES
All alcohols will have the same general properties
 All amines will have the same general properties
 All carboxylic acids will have the same general
properties


Even within a larger molecule, the functional
group will have predictable properties even if
they are not the properties of the entire molecule
WHY ARE THERE SO MANY
ORGANIC COMPOUNDS?
Carbon can form double and triple bonds
with other carbon atoms or other atoms
WHY ARE THERE SO MANY
ORGANIC COMPOUNDS?
The number of ways that carbon and other atoms
can combine is almost limitless
TWO COMPOUNDS CAN HAVE EXACTLY
THE SAME MOLECULAR FORMULAS BUT
HAVE
DIFFERENT PROPERTIES BASED ON THE
ARRANGEMENT OF THE ATOMS
Each of the statements given below is true but
John Dalton may have had trouble explaining them
with his atomic theory. Give explanations for each
of the following statements:

ethyl alcohol and dimethyl ether have the same
composition by mass—52% carbon, 13% hydrogen,
and 35% oxygen. However, they have different
melting points, boiling points, and solubility in
water.
COMPOUNDS THAT HAVE THE SAME
MOLECULAR FORMULA BUT
DIFFERENT STRUCTURAL FORMULAS
ARE CALLED STRUCTURAL ISOMERS
IN LAB, YOU HAVE ALREADY DISCOVERED SOME
OF THE PROPERTIES OF HYDROCARBONS
WHAT MAKES THE PHYSICAL PROPERTIES OF
HYDROCARBONS DIFFERENT FROM THE
PHYSICAL PROPERTIES OF INORGANIC
COMPOUNDS?
BONDING MAKES THE DIFFERENCE
Covalent Bonding
Ionic Bonding
Sharing of electrons
Transfer of electrons
CH3CH2CH2CH2CH3
Na+ + Cl- = NaCl
Organic chemistry bonding
Inorganic chemistry bonding
Partial charges & dipole
moments
Full charges, ions
Discrete molecules
Dissolve but don’t dissociate
Nonelectrolytes
Lattice structures
Dissociate in water
Electrolytes
HOW DO MELTING/BOILING POINTS
DIFFER?
Organic Compounds

Low MP and BP
Inorganic Compounds

High MP and BP
HOW DOES SOLUBILITY DIFFER?
Organic Compounds
Often insoluble in
water
 Why?
 Why not?

Inorganic Compounds
Soluble in water
 Why?

HOW DO REACTION RATES DIFFER?
Organic Compounds

Often slow to react
Inorganic Compounds

Much easier to react
COMPARISON
METHANE
Type of bonding?
 BP = -164oC
 MP = -182oC
 Slightly soluble in
water
 Flammable
 Slow to react
 Can be S, L or G
 Nonelectrolyte

NaCl
Type of bonding?
 BP = 1433oC
 MP = 801oC
 36g/100mL water
 Nonflammable
 Quick to react
 Exists at S at RT
 Electrolyte

OVERVIEW
OF
HYDROCARBONS
Hydrocarbons
Alkanes
&cycloalkanes
aliphatic
aromatic
alkenes
alkynes
WHAT ARE ALKANES?
Saturated
 Base molecule contains only C and H
 No double or triple bonds

THE FIRST FOUR ALKANES
 Methane,
 CH4,
ethane, propane, butane
C2H6, C3H8, C4H10
A MOLECULAR FORMULA
CH4, C2H6, C3H8, C4H10
GIVES THE TYPE AND NUMBER OF
ATOMS IN THE COMPOUND BUT
TELLS NOTHING ABOUT THE
STRUCTURE OF THE COMPOUND
A STRUCTURAL FORMULA
GIVES THE ACTUAL ARRANGEMENT
OF THE ATOMS IN A MOLECULE
H H H H
H
H
H H H H
A CONDENSED FORMULA
REPRESENTS THE ARRANGEMENT
OF THE ATOMS WITHOUT DRAWING
ALL THE BONDS
CH4
CH3CH3
CH3CH2CH3
CH3CH2CH2CH3
STRUCTURAL AND CONDENSED FORMULAS
ARE ESPECIALLY USEFUL WHEN
DEALING WITH STRUCTURAL ISOMERS
butane
isobutane
C4H10
C4H10
CH3CH2CH2CH3
(CH3)3CH
H
H H H H
H
H
H
H H H H
H
H
H
H
H
H
H
H
REMEMBER, REMEMBER, REMEMBER……
CARBON FORMS 4 BONDS
HYDROGEN FORMS 1 BOND
STRUCTURAL AND CONDENSED FORMULAS
ARE ESPECIALLY USEFUL WHEN
DEALING WITH ISOMERS
pentane
isopentane
C5H12
C5H12
CH3CH2CH2CH2CH3
CH3CH(CH3)CH2CH3
H
H
H H H H H
H
H
H
H
H
H
H
H H H H H
H
H
H
H
H
PRACTICE:

Write the structural formulas from the
following condensed formulas:

CH3CH2C(CH3)3

(CH3)3CC(CH3)3

(CH3)3CBr
PRACTICE:
H
H
H
H
H
H
H
H
H
H
H
H
H
Write the
condensed formulas
from the following
structural formulas:
H
H
H
H
H
H
HH
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Br
H
H
NOMENCLATURE OF ALKANES

NAME the parent compound

The first TEN straight chain alkanes are:
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Nonane
Decane
NOMENCLATURE OF ALAKNES

NUMBER the parent compound

Find the longest chain

Start numbering so that any substituents get the
lowest number possible
REPRESENTATIVE SUBSTITUENTS
--CH3
--CH2CH3
--CH2CH2CH3
--CH2CH2CH2CH3
--CH2CH2CH2CH2CH3
--F
--Br
--Cl
--I
EXAMPLES:


Name & number the longest continuous carbon
chain
Name and number the substituent
H
H
H
H
H
H
H
Br
EXAMPLES:


Name & number the longest continuous carbon
chain
Name and number the substituent
Cl
H
H
H
H
H
H
H
H
H
EXAMPLES:


Name & number the longest continuous carbon
chain
Name and number the substituent
I
H
H
H
H
H
H
H
H
H
H
H
H
I
MORE EXAMPLES:


Name & number the longest continuous carbon
chain
Name and number the substituent
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
MORE EXAMPLES:


Name & number the longest continuous carbon
chain
Name and number the substituent
H
H
H
H
H
H
H
H
H
H
H
H
H
HH
H
H
H
REACTIONS OF ALKANES

Combustion

An alkane + oxygen
gives carbon dioxide
plus water

An important side
reaction?
REACTIONS OF ALKANES

Halogenation—an alkane plus a halogen gives
an alkyl halide (substituted alkane) plus a
hydrogen halide (acid)
CH4 + Br2 → CH3-Br + HBr
CH3CH3 + Cl2 → CH3CH2-Cl + HCl
IS YOUR CYCLOALKANE A
BOAT OR A CHAIR?
IS YOUR HYDROGEN AXIAL OR
EQUATORIAL?

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