Download PowerPoint for Part 1 - Dr. Samples` Chemistry Classes

Organic Compounds and
Functional Groups
• There are more than 19 million known organic
compounds, each with its own physical and
chemical properties.
• This is very daunting, but organic compounds
may be classified into families according to
their structures.
• Members of the same families tend to have
similar properties, so grouping compounds into
families helps simplify what would initially
seem to be an bewildering number of
compounds.
• Organic compounds are classified and
grouped according to what functional
groups they contain.
• A functional group is simply a group of
atoms which is chemically reactive.
• In general, a functional group either
contains a π bond or an electronegative
or an electropositive atom(s).
• So the presence of π bonds or polar bonds
is a good indicator of chemical reactivity.
• A given functional group will undergo the same
kinds of chemical reactions in most molecules
in which they are present.
• The molecule may be very small and simple, or
it may be large, complex, and bulky: but the
common functional group will behave in an
almost identical manner.
Common Functional Groups
• The following table contains many of the
common functional groups which organic
molecules may contain.
• Note that in the Table, R is used to signify
an alkyl group, a group which contains only
sp3 C atoms and H atoms. When more than
one R is present in a General Formula, they
may or may not be different alkyl groups.
Common Functional Groups
• What are you responsible for?
• You should recognize alkenes, alkyl
halides, alcohols, amines, ethers, carboxylic
acids, ketones, aldehydes, esters, and
amides.
Functional Groups with a C-C π Bond
• There are several common groups which
contain a π C-C bond.
• What is a  bond? What is a π bond?
• Alkenes contain a double bond, while
alkynes contain a triple bond.
Functional Groups, Cont.
• Arenes, where benzene is the simplest example,
are 6-membered rings with alternating single and
double bonds (this is a simplistic explanation,
arenes have resonance structures).
• Although you know that double and triple bonds
are shorter and stronger than single bonds, the π
bond is still chemically active and can undergo
certain chemical reactions.
Functional Groups with Carbon Singly Bonded to
an Electronegative Atom
• Carbon is quite commonly bonded to an
electronegative atom like O, N, Cl, Br, I, F, or S.
• Alkyl halides have C bonded to a halogen; ethers,
alcohols have C bonded to O; amines have C
bonded to N; and thiols have C bonded to S.
• In all of these cases, the end result is a polar bond
with the C having a δ+ charge. This partial charge
separation leads to chemical reactivity.
Carbonyl Functional Groups
• There is a common class of compounds where a C
atom is double bonded to O, or the C=O group.
• It’s generic name is the carbonyl group.
• Common carbonyl compounds include amino
acids, fatty acids, and soaps.
• There are several types of carbonyl compounds as
seen in the Table.
Carbonyl Functional Groups
– carboxylic acids
– esters (sweet smelling compounds found in
fruits, etc., and used in perfumes)
– ketones
– aldehydes (usually foul smelling like
formaldehyde)
– amides (peptides and proteins are amides)
Carbonyl Functional Groups
– acid halides
– acid anhydrides
– In all of these groups, the C=O bond is polar
with the O atom having a δ- charge and the
C atom having a δ+ charge.
Properties of Alkanes
• Alkanes are hydrocarbons (C, H
compounds) which contain only sp3
hybridized C atoms.
• Thus, they contain only single bonds.
• Because of this, they are also called
saturated hydrocarbons, as they are
saturated with hydrogen.
• They have a CnH2n+2 general formula
(except cycloalkanes).
Properties of Alkanes
• In general, alkanes are not very reactive.
• They will react with oxygen, halogens, and a few
other substances.
• Alkanes are common fuel sources for cars, houses,
etc.
• Common alkane fuels are methane, propane,
butane, and of course think of your octane rating
at the gas pump!
Properties of Alkanes
• When an alkane (or any hydrocarbon) combusts,
the two ideal products are carbon dioxide and
water, although carbon monoxide and other
unwanted products are made as well.
• Of course, combustion reactions are exothermic,
so a great deal of useful heat is given off as well.
• This heat is called the heat of combustion, ΔHcomb.
• As you might expect, as you increase the number
of C atoms in the alkane, there is more to burn,
and more heat is given off.
Alkane Halogenation
• Alkanes also react with halogens in a
reaction called halogenation.
• UV light acts as a catalyst in starting the
reaction.
• One or more halogen atoms may be added
to the alkane, so there are a variety of
products made.
Polarity and Intermolecular Forces
• Alkanes are nonpolar molecules as they contain
only C-C and C-H single bonds.
• So the intermolecular forces acting between
molecules are weak London Dispersion Forces.
• As you may remember, London Dispersion Forces
get stronger as the molar mass or molecule size
increases.
London Forces & BPt and MPt
• alkanes with a carbon chain up to 4 are gases at
room temperature
• alkanes with a C chain of up to 17 are liquids
• alkanes with a C chain of over 17 are solids.
London Forces & Molecular Shape
• You may also remember, that the bulkiness or shape of the
molecule also affects the strength of the London
Dispersion Forces.
• The closer 2 or more molecules may come together, the
stronger the London Forces will be, so the higher the
boiling and melting point.
• So if a molecule is very bulky with lots of alkyl group
branching, molecules can’t get as close together.
• Continuous-chain hydrocarbons have higher boiling and
melting points than do what we call branched-chain
alkanes.
Alkane Solubilities
• Because alkanes are nonpolar, they are not
very soluble in water or other very polar
solvents.
• Instead, they are soluble in relatively
nonpolar solvents like benzene, ethers, etc.
• The densities of alkanes are lower than
water, which you should know as oil and
gas float on water!
Cycloalkanes
• Cycloalkanes are ring structure where there
are no end C; or you could say that the two
end C have joined to form a ring.
• Because of this extra C-C bond, 2 H atoms
are lost, so the general formula is CnH2n.
• But, just like alkanes, they contain only sp3
hybridized C atoms.
Properties of Cycloalkanes
• The properties of cycloalkanes are very
similar to those of alkanes.
• However, if you use a molecular model kit
and make some cycloalkanes, you will
notice a few differences.
• Cycloalkanes, particularly small
cycloalkanes, are highly symmetric.
Properties of Cycloalkanes
• You should also notice that cycloalkanes do not
rotate around C-C bonds as freely as regular
alkanes.
• In open-chain alkanes, there is free rotation around
all of the C-C bonds.
• But in cycloalkanes, this C-C rotation is greatly
hindered by the closed ring: if there were free
rotation around the C-C bond, the ring might be
broken.
Properties of Cycloalkanes
• The smallest cycloalkanes, C3 to C6 or C7, have
rigid rings with little C-C rotation possible.
• Because of this rigidity, these rings are strained,
and they are more reactive than larger rings.
• As cycloalkanes get larger, the rigidity of the ring
decreases, the ring strain decreases, and there is
more freedom of rotation.
• Large cycloalkanes are floppy, and are virtually
identical to open-chain molecules.
Properties of Cycloalkanes
• Because of their greater symmetry and
hindered C-C rotation, cycloalkanes
generally have higher melting points,
boiling points, and densities than openchain alkanes.
• See the following Table for examples.
Compound
B.Pt.
M.Pt.
Pentane
(C5H12)
36.1
-129.8
Density
(g/mL)
0.5582
Cyclopentane 49.3
(C5H10)
Octane
125.7
(C8H18)
-93.9
0.7457
-56.8
0.7026
Cyclooctane
(C8H16)
14.3
0.8349
150.0