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General, Organic & Biological
Chemistry
Ch 10 &11 New Book
Introduction to Organic
Chemistry: Alkanes
12.1 The Nature of Organic
molecules
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Organic chemistry: The chemistry of carbon
compounds.
Carbon is tetravalent; it always form four
bonds.
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Organic molecules have covalent bonds.
Organic molecules contain polar covalent
bonds when carbon bonds to an
electronegative element on the right side of
the periodic table.
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Carbon can form multiple covalent bonds by
sharing more than two electrons with a
neighboring atom.
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Organic molecules have specific three
dimensional shapes.
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Organic molecules often contain hydrogen,
nitrogen, and oxygen in addition to carbon.
Nitrogen can form single, double, or triple
bonds to carbon; oxygen can form single and
double bonds.
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12.2 families of Organic Molecules:
Functional groups
More than 18 millions organic compounds, that are
known today, are classified into just a few general
families on the basis of chemistry that follows a
simple pattern.
Functional group: A group of atoms within a large
molecule that has a characteristic structure and
chemical behavior. Functional groups allow us to
group vast number of organic molecules in to few
classes, Table 12.1.
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In Table 12.1, the first four families are
hydrocarbons – organic compounds that contain only
carbon and hydrogen.
- Alkanes have only single bonds.
- Alkenes contain a carbon-carbon double bond
functional group.
- Alkynes contain a carbon-carbon triple bond
functional group.
- Aromatic compounds contain a six-membered
ring of carbon atoms with three alternating
double bonds.
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In Table 12.1, the next four families have functional
groups that contain only single bonds and have a
carbon atom bonded to an electronegative atom.
- Alkyl halides have a carbon-halogen bond;
- Alcohol have a carbon-oxygen bond;
- Ethers have two carbons bonded to the same
oxygen atom; and
- Amines have a carbon-nitrogen bond.
The remaining families have functional groups that
contain a carbon-oxygen double bond; aldehydes,
ketones, carboxylic acids, anhydrides, esters, and
amides.
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12.3 The Structure of Organic
Molecules: Alkanes and Their Isomers
Alkanes: A hydrocarbon that has only single bonds.
Straight chain alkanes: An alkane that has all its
carbons connected in a row.
Branched chain alkanes: A alkane that has a
branching connection of carbons.
Isomers: Compounds with same molecular formula
but different structures.
Constitutional isomers: Compounds with same
molecular formula but different connections among
their atoms.
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There is only one possible way that the carbons
in methane (CH4), ethane (C2H6), and propane
(C3H8) can be arranged.
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However, carbons in butane (C4H10) can be
arranged in two ways; four carbons in a row
(linear alkane) or a branching (branched
alkane). These two structures are two
constitutional isomers for butane. Number of
possible structures increases with the number
of carbons in the molecule.
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Different constitutional isomers are completely
different compounds.
They have different
structures, different physical properties such as
melting point and boiling point, and may have
different physiological properties.
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12.4 Drawing Organic Structures
Condensed structure: A shorthand way of
drawing structures in which carbon-carbon and
carbon-hydrogen bonds are understood rather
than shown.
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12.5 The Shapes of Organic Molecules
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Molecules joined by a carbon-carbon single bonds
are free to spin around the bond, giving rise to an
infinite number of possible three dimensional
geometries, or conformations.
Fig 12.2 The structure of butane can be shown in
several different ways.
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At any moment, however, most
molecules are in the least crowded
conformation.
As long as any two structures show
identical connections between atoms,
they represent identical compound no
matter how the structures are drawn.
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12.6 Naming Alkanes
The system of naming (Nomenclature) used now
is devised by the International Union of Pure and
Applied Chemistry, or known as IUPAC. In the
IUPAC system for organic compounds, a name
has three parts;
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Substituents: An atom or group of atoms
attached to a parent compound.
Alkyl group: The part of an alkane that
remains when a hydrogen atom is
removed.
Remove one hydrogen from CH4  CH3 (Methyl group.)
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Both methane and ethane have only one
kind of hydrogen. It does not matter which of
the hydrogen from methane or ethane is
removed, it will produce the same methyl or
ethyl group.
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Propane has two different kinds of
hydrogen. Removing one of the 6 hydrogen
from two CH3 produces propyl group whereas
removal of one of the two hydrogen from CH2
produces isopropyl group.
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Rules for Naming Alkanes
1- See new book p. 327 and 333
2- Straight Chains- # so that groups
(substituents) have the lowest #’s; but name
alphabetically. **Only the prefix iso is used
for alphabetizing. (**And cyclo, if it is used
as a substituent)
3-Cyclic- A) If only 1 substituent on the ring,
no number is needed. B) If 2 there are 2
substituents, # the C atoms beginning w/
the C with substituent that’s lowest in
alphabetical order. C) If 3 or more, number
the sub. to give them the lowest numbers,
but list in alphabetical order
Primary carbon atom: A carbon atom
with one other carbon attached to it.
Secondary carbon atom: A carbon atom
with two other carbons attached to it.
Tertiary carbon atom: A carbon atom
with three other carbons attached to it.
Quaternary carbon atom: A carbon atom
with fourother carbons attached to it.
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Straight chain alkanes are named by counting
the number of carbon atoms and adding the
family suffix –ane.
Branched chain alkanes can be named
following four steps:
Step 1: Name the main chain. Find the
longest continuous chain of carbons, and name
the chain according to the number of carbon
atoms it contains.
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Step 2: Number the carbon atoms in the main
chain, beginning at the end near the first branch
point.
Step 3: Identify the branching substituents, and
number each according to its point of attachment
to the main chain.
Step 4: Write the name as a single word, using
hyphens to separate the numbers from the
different prefixes and commas to separate
numbers if necessary. Cite different substituents
in alphabetical order. Use di-, tri-, etc for two or
three identical substituents present in the
molecule.
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12.7 Properties of Alkanes
Melting points and boiling points of straight chain
alkanes increases with molecular size.
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The first four alkanes, methane, ethane, propane,
and butane are gases.
Alkanes with 5-15 carbon atoms are liquids.
Alkanes with 16 or more carbon atoms are low
melting waxy solids.
Alkanes are insoluble in water but soluble in
nonpolar organic solvents, including other
alkanes.
Alkanes are generally less dense than water as
result they float on water.
Low molecular-weight alkanes are volatile and
their vapors are highly flammable.
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12.8 Reactions of Alkanes
Alkanes don’t react with acids, bases, or most other
common laboratory reagents.
Their only major
reactions are with oxygen and with halogens.
Combustion: Reaction of alkanes with oxygen. Carbon
dioxide and water are produced in this combustion
reaction.
Halogenation reaction: Replacement of a hydrogen of
alkanes by a chlorine or bromine.
Initiation of
halogenation reaction requires heat or light. Complete
chlorination of methane produces carbon tetrachloride.
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12.9 Cycloalkanes
Cycloalkanes: An alkane that contains a ring of carbon
atoms. Ring sizes from 3 carbons to 30 or higher are
known.
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Cyclopropanes and cyclobutanes are less stable
since the C-C-C bond angles are 60o and 90o
respectively, much compressed from the
normal tetrahedral bond angle of 109.5o.
Cyclopentane has nearly ideal bond angle as a
result it is stable.
Cyclohexane has a puckered non-planar
structure called a chair conformation. In chair
conformation, carbon atoms have 109o bond
angles and is very stable.
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Cyclopropanes and cyclobutanes are less stable
since the C-C-C bond angles are 60o and 90o
respectively, much compressed from the normal
tetrahedral bond angle of 109.5o.
Cyclopentane has nearly ideal bond angle as a
result it is stable.
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12.10 Drawing and Naming
Cycloalkanes
Cycloalkanes are represented by polygons. A tyriangle
represents cyclopropane, a square represents
cyclobutane, a pentagon represents cyclopentane, and
so on.
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Line structure: A shorthand way of
drawing structures in which atoms aren’t
shown; instead a carbon atom is
understood to be at each intersection of
lines and hydrogens are filled mentally.
Cycloalkanes
are
named
by
a
straightforward extension of the rules for
open-chain alkanes. In most cases, only
two steps are needed:
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Step 1: use the cycloalkane name as the
parent.
Step 2: Number the substituents starting
at the group that has alphabetical
priority, and proceed around the ring in
the direction that gives the second
substituent the lower possible number.
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Isomers
• Constitutional: Same molecular formulas, but
connectivity (and properties) are different (expentane and 2-methylbutane)
• Stereoisomers: 1- Geometrical (cis/trans) in
cycloalkanes; 2- Enantiomers- chiral
(asymmetrical) carbon(s) that are mirror
images. Usually designated as D (right) or L
(left) or R and S
• **Note- there are other types of isomers, but
these are the only ones you have to know at
this point
Chapter Summary
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Organic compounds are classified into various
families according to the functional group
they contain.
A functional group is a group of atoms that
has characteristic structure and chemical
reactivity.
Isomers are compounds that have the same
molecular formula but different structures.
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Chapter Summary Contd.
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Organic molecules are represented by structural
formula showing bonds between the atoms, or by
condensed formula showing only the atoms and
not the bonds, or by line structure in which the
carbon skeleton is shown by lines.
Hydrocarbons are organic molecules containing
only carbon and hydrogen atoms.
Alkanes or open chain hydrocarbons, contain only
single bonds.
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Chapter Summary Contd.
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Cycloalkanes are organic compounds
containing ring of carbon atoms.
Alkanes are not soluble in water. They are
soluble in non-polar organic solvents.
They are not toxic.
They react mainly with oxygen (combustion
reaction) and halogens (halogenation
reaction).
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End of Chapter 12
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