Lecture8-notes

Lecture8-notes - 9/15/09


Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 9/15/09
 Organic
compounds
are
classified
into
families
(classes),
each
member
of
which
has
a
 common
characteristic
chemical
behavior.
 All
alkenes
react
with
bromine.
 All
carboxylic
acids
are
acidic.
 All
amines
are
basic.
 Characteristic
chemical
behaviors
arise
because
all
of
the
members
of
a
particular
family
 possess
a
common
functional
group,
which
dictates
the
behavior
of
the
molecule.
 Organic
Functional
Groups
 1
 9/15/09
 Organic
Functional
Groups
 Organic
Functional
Groups
 2
 9/15/09
 Organic
Functional
Groups
 Organic
Functional
Groups
 3
 9/15/09
 Organic
Functional
Groups
 Organic
Functional
Groups
 4
 9/15/09
 Organic
Functional
Groups
 Organic
Functional
Groups
 5
 9/15/09
 Organic
Functional
Groups
 Organic
Functional
Groups
 6
 9/15/09
 Organic
Functional
Groups
 7
 9/15/09
 • The
only
bonds
found
in
alkanes
are
carbon–carbon
and
carbon–hydrogen
single
bonds.
 • Alkenes,
alkynes,
and
aromatics
contain
multiple
bonds,
two
adjacent
carbon
atoms
that
 share
more
than
one
bond
between
them.

 • An
alkene
has
a
carbon–carbon
double
bond,
two
bonds
between
a
pair
of
adjacent
 carbon
atoms.

 • An
alkyne
has
a
carbon–carbon
triple
bond,
three
bonds
between
a
pair
of
adjacent
 carbon
atoms.

 • An
aromatic
has
six
carbon
atoms
in
a
cyclic
arrangement
with
alternating
single
and
 double
bonds.
 • An
alcohol
contains
a
hydroxyl
group,
an
OH
group
attached
to
a
carbon
atom.
 • An
ether
contains
an
oxygen
attached
directly
to
two
different
carbons.
 • An
amine
contains
an
amino
group,
an
NH3
group
attached
to
a
carbon
atom.
(In
some
 amines,
an
NH
or
an
N
is
attached
to
two
or
three
carbon
atoms,
respectively.)
 8
 9/15/09
 • Aldehydes,
ketones,
carboxylic
acids,
esters,
and
amides
possess
the
carbonyl
group,
a
 carbon–oxygen
double
bond,
but
differ
in
the
atom
or
group
of
atoms
connected
to
the
 carbon
of
the
carbonyl
group.

 • The
carbonyl
carbon
of
an
aldehyde
is
directly
connected
to
at
least
one
hydrogen.

 • The
carbonyl
carbon
of
a
ketone
is
directly
connected
to
carbon
atoms,
not
 hydrogen.

 • The
carbonyl
carbon
of
carboxylic
acids
and
esters
is
connected
by
a
single
bond
to
an
 oxygen,
but
these
families
differ
in
what
is
connected
to
that
oxygen.

 • In
carboxylic
acids,
a
hydrogen
is
connected
to
the
oxygen;
in
esters,
the
oxygen
is
 connected
to
a
second
carbon
atom.

 • An
amide
has
a
nitrogen
connected
to
the
carbonyl
carbon.
 Forces
between
molecules
at
the
molecular
level
are
called
secondary
forces.
 Secondary
forces
can
be
divided
into
two
types:
 • Intermolecular
forces
or
van
der
Waals
forces
between
two
molecules.

These
forces
are
those
 responsible
for
holding
solids
and
liquids
together.
 • Intramolecular
forces
between
different
parts
of
the
same
molecule.

These
forces
are
 responsible
for
the
correct
folding
of
protein
and
other
large
biomolecules.
 • Secondary
forces
are
only
10‐20%
as
strong
as
covalent
or
ionic
bonds.
 9
 9/15/09
 Dipole‐Dipole
Interactions
 • Molecules
containing
permanent
dipoles
(polar
molecules)
attract
each
other
as
well
as
 other
molecules
containing
dipole
moments.
 • The
attractions
between
δ+
and
δ–
parts
of
the
molecules
are
strong
because
the
charges
 are
close
together.
The
repulsive
forces
between
like
charges
are
smaller
because
the
unlike
 charges
are
farther
apart.
 • These
forces
are
called
dipole‐dipole
forces
and
occur
in
between
polar
molecules
such
as
 methyl
chloride,
CH3Cl,
or
chloroform,
CHCl3.
 • Water,
H2O,
a
polar
substance,
is
a
liquid
at
room
temperature
while
methane,
a
non‐polar
 substance,
CH4,
is
a
gas.
Water
molecules
are
bent
and
have
a
large
dipole
moment
while
 methane
molecules
are
symmetrical
and
have
no
net
dipole
moment.
 10
 9/15/09
 London
Forces
of
Interaction
 • Nonpolar
molecules,
such
as
methane,
will
condense
into
liquids
at
low
temperatures,
so
 some
type
of
force
must
exist
between
individual
non‐polar
molecules.
 • At
any
instant
in
time,
the
electrons
moving
about
the
atoms
in
a
molecule
may
be
 unequally
distributed
with
respect
to
the
protons
in
the
molecule.
This
results
in
a
 temporary,
small
dipole
moment.
(Think
of
a
helium
atom
with
both
electrons
on
one
side
 of
the
molecule).
 • This
brief,
small
dipole
moment
affects
the
electron
distribution
in
neighboring
molecules
 in
such
a
way
to
create
an
attractive
force.
 • The
attractive
force
due
to
these
temporary
dipoles
is
called
a
London
force
and
occurs
in
 all
molecules,
polar
or
not.
 • The
strength
of
the
London
force
can
range
from
very
small
to
about
that
of
a
regular
 dipole‐dipole
interaction.
 • The
magnitude
of
London
forces
in
nonpolar
molecules
is
reflected
in
their
boiling
points.
 11
 9/15/09
 • Hydrogen
bonds
are
special
dipole‐dipole
interactions
involving
hydrogen
and
one
of
 these
elements:
oxygen,
nitrogen,
or
fluorine.
 • The
polarity
of
an
O‐H,
N‐H,
or
F‐H
bond
is
very
high,
which
leads
to
an
especially
strong
 dipole‐dipole
interaction:
 • Hydrogen
bonds
form
between
identical
molecules,
as
in
liquid
water,
or
between
 different
molecules
in
mixtures,
such
as
ammonia,
NH3,
dissolved
in
water.
 • Hydrogen
bonds
are
weaker
than
covalent
bonds
and
are
often
denoted
by
dotted
lines
 connecting
one
molecule
to
the
other:
 O–H∙∙∙N
 • The
hydrogen
atom
acts
as
a
“glue”
bonding
the
oxygen
and
nitrogen
atoms
together.
 12
 9/15/09
 The
value‐normal
boiling
point
of
a
substance
is
largely
determined
by
the
types
of
 secondary
forces
between
molecules
in
the
liquid
state:
 • London
forces
 • Dipole‐dipole
forces
 • Hydrogen
bonds
 • Hydrogen‐bonding
substances
interact
by
all
three
types
of
forces.
 • Polar
substances
interact
by
dipole‐dipole
and
London
forces.
 • Nonpolar
substances
interact
by
London
forces
only. 

 13
 9/15/09
 In
organic
compounds,
the
strength
of
the
secondary
forces
between
molecules
depend
 upon:
 Family
(type
of
secondary
force)
 Molecular
mass
 Molecular
shape
 Family:
 The
family
determines
what
chemical
bonds
are
present,
whether
the
bonds
are
polar
 or
non‐polar,
and
whether
there
is
hydrogen
bonding.
 The
order
of
secondary
forces
is:
 Hydrogen
bonding
>
dipole‐dipole
>
London
 All
molecules
possess
London
forces.
Polar
molecules
possess
dipole‐dipole
forces
 as
well.
Hydrogen
bonds
are
only
present
in
organic
molecules
when
O‐H
or
N‐H
 bonds
are
present.
 • The
highest
boiling
point
within
the
nonpolar
group
of
molecules
is
associated
with
the
 largest
molecule.
 • A
large
molecule
has
many
electrons
capable
of
creating
temporary
dipoles
in
different
 parts
of
the
molecule
at
the
same
time.
 14
 9/15/09
 Trends
in
the
physical
properties
(melting
points
and
boiling
points)
of
compounds
can
be
 predicted
by
answering
two
questions:
 • Are
the
compounds
polar
or
nonpolar?
 • Can
the
compounds
form
hydrogen
bonds?
 15
 9/15/09
 Molecular
mass:
 For
any
series
of
compounds
in
the
same
organic
family,
London
forces
increase
with
 increasing
molar
mass.


 Molecular
shape:


 For
compounds
within
the
same
family
and
having
the
same
or
close
molecular
 masses,
the
order
of
boiling
points
is:
 Cycloalkane
>
straight‐chain
alkane
>
branched
alkane
 Molecules
that
are
able
to
pack
closely
together
 experience
much
larger
London
forces
than
 unsymmetrical
molecules.
 16
 9/15/09
 Density
 Molecules
having
large
secondary
forces
pack
together
tightly,
resulting
in
greater
densities.
 Water
(hydrogen
bonding)
has
a
density
of
1.0
g /ml.
Liquid
alkanes
have
densities
of
 0.7‐0.8
g /ml,
depending
upon
molar
mass.
 17
 9/15/09
 Solubility
 A
particular
solute
will
dissolve
in
a
solvent
only
if
the
solute‐solute
secondary
forces
are
 similar
to
the
solvent‐solvent
secondary
forces.
 Like
dissolves
like.
 Physical
Properties
of
Organic
Compounds
 •  Alkanes
 –  Melting
and
boiling
points
increase
with
increasing
 molecular
weight
within
a
homologous
series.

 Compound
 Formula
 MW

 (g /mol)
 16
 72
 142
 212
 282
 mp
(ºC)
 bp
(ºC)
 Methane
 Pentane
 Decane
 Pentadecane
 Eicosane
 CH4
 CH3(CH2)3CH3
 CH3(CH2)8CH3
 CH3(CH2)13CH3
 CH3(CH2)18CH3
 –182
 –130
 –30
 10
 37
 –164
 36
 174
 271
 343
 18
 9/15/09
 Physical
Properties
of
Organic
Compounds
 •  Alkanes
 –  Boiling
points
decrease
with
chain
branching.

 Physical
Properties
of
Organic
Compounds
 19
 9/15/09
 20
 ...
View Full Document

Ask a homework question - tutors are online