Transcript Organic Chem Functional Groups

Chapter 22
“Functional Groups”
Functional Groups
Most organic chemistry
involves substituents
often contain O, N, S, or P
also called “functional
groups”- they are the
chemically functional part
of the molecule, and are
the non-hydrocarbon part
Functional Groups
Functional group - a specific
arrangement of atoms in an
organic compound, that is
capable of characteristic
chemical reactions.
What is the best way to
classify organic compounds?
By their functional
groups.
Functional Groups
The symbol “R” is used to
represent any carbon chains
or rings
Important: Table 22.2, page
589 shows some of the major
functional groups - KNOW
THESE.
Halogen Substituents
Halocarbons - class of organic
compounds containing
covalently bonded fluorine,
chlorine, bromine, or iodine
General formula: R-X (X =
halogen)
Naming? Name parent as
normal, add the halogen as a
substituent (or prefix)
Halogen Substituents
The more highly halogenated
the compound is, the higher
the b.p.
Few halocarbons found in
nature
but, readily prepared and
used
halothane and also the
hydrofluorocarbons
Substitution Reactions
Organic reactions often much
slower than inorganic reactions
must break strong covalent
bond
trying to find new catalysts to
use
Substitution - an atom (or
group of atoms) replaces
another atom or group of atoms
Substitution Reactions
A halogen (shown as “X”) can
replace a hydrogen to make a
halocarbon:
R-H + X2  R-X + HX
Sunlight is often a sufficient
catalyst:
CH4 + Cl2
UV light
→
CH3Cl + HCl
Substitution Reactions
Treating benzene with a halogen?
Examples on Page 601
C6H6(l) + Cl2(g) → C6H5Cl(l) + HCl (g)
Halogens on carbon chains are
readily displaced by hydroxide ions
(OH1-) to make an alcohol + a salt:
R-X + OH1-  R-OH + X1CH3-Cl + NaOH  CH3-OH + NaCl
Methanol + sodium chloride
Substitution Reactions
CH3-I + KOH  CH3-OH + KI
Iodomethane
Methanol
CH3CH2Br + NaOH  CH3CH2OH + NaBr
Bromoethane
Ethanol
Alcohols
Alcohols - 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? (covalent bonding with
the carbon- not ionic with a metal like bases)
Alcohols
Aliphatic alcohols classified into
categories according to the number of
R groups attached to the carbon with
the hydroxyl
1 R group: primary alcohol
2 R groups: secondary alcohol
3 R groups: tertiary alcohol
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.
Alcohols
The hydroxyl is given the
lowest position number
Alcohols containing 2, 3,
and 4 of the -OH
substituents are named
diols, triols, and tetrols
respectively
Alcohols
Common names:
similar to halocarbons,
meaning name the alkyl
group, then followed by
the word alcohol
One carbon alcohol =
methyl alcohol
Alcohols
More than one -OH substituents
are called glycols (ethylene glycol?)
** Examples on page 590**
Phenols - compounds in which a
hydroxyl group is attached directly
to an aromatic ring. Cresol is the
common name of o, m, and p
isomers of methylphenol
Properties of Alcohols
Much like water, alcohols are
capable of hydrogen bonding
between molecules
this means they will boil at a
higher temp. than alkanes and
halocarbons with a comparable
number of atoms
Properties of Alcohols
Alcohols are derivates of water;
the -OH comes from water, and
thus are somewhat soluble
Alcohols of up to 4 carbons are
soluble in water in all proportions;
more than 4 carbons are usually
less soluble, because the longer
carbon chain is more nonpolar
Properties of Alcohols
Many aliphatic alcohols used in
laboratories, clinics, and industry
Isopropyl alcohol (2propanol) is rubbing alcohol;
used as antiseptic, and a base
for perfume, creams, lotions,
and other cosmetics
Ethylene glycol (1,2-ethanediol) commonly sold as “antifreeze”
Properties of Alcohols
Glycerol (1,2,3-propanetriol) used as a moistening agent
in cosmetics, foods, and
drugs; also a component of
fats and oils
Ethyl alcohol (ethanol) used
in the intoxicating beverages;
also an important industrial
solvent
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!
Addition Reactions
The carbon-carbon single
bond is not easy to break
In double bonded alkenes, it
is easier to break a bond
Addition reaction- substance
is added at the double or
triple bond location, after it is
broken
Addition Reactions
Addition of water to an alkene
is a hydration reaction usually occurs with heat and an
acid (such as HCl or H2SO4
acting as a catalyst)
Note sample in the middle of
page 590 for the formation of
ethanol from ethene + water
Addition Reactions
Addition of hydrogen to
produce an alkane is a
hydrogenation reaction,
which usually involves a
catalyst such as Pt or Pd
common application is the
manufacture of margarine
from unsaturated vegetable
oils (making them solid from
a liquid)
Ethers
A class of organic compounds
in which oxygen is bonded to 2
carbon groups: R-O-R is
formula
Naming? The two R groups are
alphabetized, and followed by
ether
Two R groups the same? Use
the prefix di-
Ethers
Diethyl ether is the one
commonly called just “ether”
was the first reliable general
anesthetic
dangerous- highly flammable,
also causes nausea
ethers are fairly soluble in water
Aldehydes and Ketones
Review:
alcohol has an oxygen
bonded to a carbon group
and a hydrogen
ether has an oxygen bonded
to two carbon groups
An oxygen can also be
bonded to a single carbon
by a double bond
Aldehydes and Ketones
The C=O group is called the
“carbonyl group”
it is the functional group in both
aldehydes and ketones
Aldehydes - carbonyl group
always joined to at least one
hydrogen (meaning it is always
on the end!)
Aldehydes and Ketones
Ketones - the carbon of
the carbonyl group is
joined to two other
carbons (meaning it is
never on the end)
Aldehydes and Ketones
Naming?
Aldehydes: identify longest chain
containing the carbonyl group, then
the -e ending replaced by -al, such
as methanal, ethanal, etc.
Ketones: longest chain w/carbonyl,
then new ending of -one; number
it?
propanone, 2-pentanone, 3pentanone
Aldehydes and Ketones
Neither can form intermolecular
hydrogen bonds, thus a much
lower b.p. than corresponding
alcohols
wide variety have been isolated
from plants and animals; possible
fragrant odor or taste; many
common names
Aldehydes and Ketones
Benzaldehyde
Cinnamaldehyde
Vanillin
See page 592 for structures of
these 3
Methanal (the common name is:
formaldehyde)
40% in water is formalin, a
preservative
Aldehydes and Ketones
Propanone (common: acetone)
is a good solvent; miscible with
water in all proportions
why is it a good substance
used in nail-polish removers?
(a powerful solvent-able to
dissolve both polar & nonpolar)
The Carboxylic Acids…
Also have a carbonyl group (C=O),
but is also attached to a hydroxyl
group (-OH) = “carboxyl” group
general formula: R-COOH
weak acids (ionize slightly)
Named by replacing -e with -oic and
followed by the word acid
methanoic acid; ethanoic acid
Carboxylic Acids
Abundant and widely distributed
in nature, many having a Greek
or Latin word describing their
origin
acetic acid (ethanoic acid) from
acetum, meaning vinegar
many that were isolated from
fats are called fatty acids
The Esters…
General formula: RCOOR
Derivatives of the carboxylic acids, in
which the -OH from the carboxyl group
is replaced by an -OR from an alcohol:
carboxylic acid + alcohol  ester + water
many esters have pleasant, fruity
odors- banana, pineapple, perfumes
Esters
Although polar, they do not
form hydrogen bonds (reason:
there is no hydrogen bonded to
a highly electronegative atom!)
thus, much lower b.p. than
the hydrogen-bonded
carboxylic acids they came
from
Esters
Can be prepared from a
carboxylic acid and an
alcohol; usually a trace of
mineral acid added as
catalyst (because acids are
dehydrating agents)
Note equation on p. 593
Esters
Naming? It has 2 words:
1st: alkyl attached to single
bonded oxygen from alcohol
2nd: take the acid name,
remove the -ic acid, add -ate
example on top of page 593
Amines
Amines contain a basic nitrogen
atom with a lone pair.
Amines are derivatives of ammonia,
where in one or more hydrogen atoms
have been replaced by a substituent
such as an alkyl group.
Important amines include amino
acids, biogenic amines,
trimethylamine, and aniline
Primary amine Secondary amine Tertiary amine
Isomers
Isomers are compounds with the same molecular
formula but different structural formulas
A simple example of isomerism is given by the
formula C3H8O (or C3H7OH) and occurs as two
isomers: 1 -propanol and 2- propanol
Note that the position of the oxygen atom differs
between the two: it is attached to an end carbon in
the first isomer, and to the center carbon in the
second.
There is, however, another isomer of C3H8O which
has significantly different properties: methyl-ethylether.
Unlike the isomers of propanol, the ether has an
oxygen connected to two carbons rather than to
one carbon and one hydrogen.
Geometric
Isomers
In one, the two chlorine atoms are locked on
opposite sides of the double bond. This is
known as the trans isomer. (trans : from latin
meaning "across" - as in transatlantic).
In the other, the two chlorine atoms are locked
on the same side of the double bond. This is
know as the cis isomer. (cis : from latin
meaning "on this side"
cis & trans isomers differ
from each other in their
physical properties and to a
lesser extent their chemical
properties.
Optical Isomers (enantiomers)
These two models each have the same groups joined to the central
carbon atom, but still manage to be different:
Obviously as they are drawn, the orange and blue groups aren't
aligned the same way. Could you get them to align by rotating one
of the molecules? The next diagram shows what happens if you
rotate molecule B.
They still aren't the same - and there is no way that you can rotate
them so that they look exactly the same. These are isomers of each
other.
They are described as being non-superimposable in the sense
that you couldn't slide one molecule exactly over the other one.
Something would always be pointing in the wrong direction.
These molecules are said to be chiral.
Chiral molecules have the same physical properties, but b/c they
differ in the 3-D structue they may show different physiological
properties. (Aleve,
Oxidation- Reduction Reactions
All of the previous classes of
organic compounds are related by
oxidation and reduction reactions
What is oxidation-reduction?
Oxidation: the gain of oxygen,
loss of hydrogen, or loss of e-1
Reduction: the loss of oxygen,
gain of hydrogen, or gain of e-1
Oxidation- Reduction Reactions
Oxidation and reduction reactions
(sometimes called redox) are
coupled- one does not occur
without the other
The number of Oxygen and
Hydrogen attached to Carbon
indicates the degree of oxidation
Oxidation- Reduction Reactions
The fewer the # of H on a C-C bond,
the more oxidized the bond
Thus, a triple bond is more
oxidized than a double bond and a
single bond
An alkane is oxidized (loss of H) to
an alkene, and then to an alkyne
Oxidation- Reduction Reactions
Loss of hydrogen is called a
dehydrogenation reaction
may require strong heating
and a catalyst
Oxidation- Reduction Reactions
Methane can be oxidized in steps
to carbon dioxide
methane  methanol 
methanal  methanoic acid 
CO2
the more reduced (more H) a
carbon compound, the more
energy it can release upon
oxidation