Transcript Unsaturated Hydrocarbons

UNSATURATED HYDROCARBONS
HYDROCARBONS
SATURATED
PARAFFINS
ALKANES
UNSATURATED
CYCLOALKANES
H H
ALKENES
H
C
H C C H
H
H H
RING WITH CONJUGATED
DOUBLE BONDS
ALKYNES
H C C H
H
C
H
AROMATICS
H
H
H
CONJUGATED
DOUBLE BONDS
Chemistry 21A
ISOLATED
DOUBLE BONDS
C
C
C
C
C
C
H
H
H
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
ethene (ethylene)
propene (propylene)
1-butene (1-butylene)
cis-2-butene
Chemistry 21A
chloroethene (chloroethylene)
vinyl chloride
trans-2-butene
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
cyclopropene
C23H46
Muscalure, or cis-9-tricosene, is the
sex pheromone of the female common
housefly (Musca domestica)
butadiene
cyclopentadiene
cycloheptene
cyclooctene
propan-1,2-diène
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Alkane
R–CH2–CH2–R
CnH2n+2
This is the maximum H/C ratio for
a given number of carbon atoms.
Alkene
R–CH=CH–R
CnH2n
Each double bond reduces the
number of hydrogen atoms by 2.
Alkyne
R–C≡C–R
CnH2n-2
Each triple bond reduces the
number of hydrogen atoms by 4.
Each ring reduces the
number
of hydrogen atoms by 2
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
p-orbitals
s-orbitals
sp2-orbitals
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
In sp2 hybridization the 2s
orbital is mixed with only two of
the three available 2p orbitals:
forming a total of 3 sp2 orbitals with
one p-orbital remaining.
In ethylene (ethene) the two carbon
atoms form a σ bond by overlapping
two sp2 orbitals and each carbon atom
forms two covalent bonds with
hydrogen by s–sp2 overlap all with
120° angles.
The π bond between the carbon atoms
perpendicular to the molecular plane
is formed by 2p–2p overlap.
Chemistry 21A
π-bond
Ethylene (ethene), showing
the pi bond in green
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Since sp2 hybrid orbitals are always in the same plane, the entire ethylene molecule is planar.
Cis-/trans- isomerism are the consequence of the planarity
of all atoms bonded to double-bonded (C=C) carbon atoms.
cis-2-butene
Chemistry 21A
trans-2-butene
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
cyclopropene
H2
C
H2C
H2C
All are cis
cycloheptene
H3C
H
CH3
H
cis-2-butene
Chemistry 21A
H3C
H
CH
C C
H2 H2
H
H3C
H
CH3
H3C
H
trans-2-butene
CH
methylpropene
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
C18H34O2
Elaidic acid is a trans unsaturated
fatty acid often found in partially
hydrogenated vegetable oils.
Oleic acid is a cis unsaturated
fatty acid that comprises
55–80% of olive oil.
C18H36O2
Stearic acid is a saturated fatty acid found in animal fats
and is the intended product in full hydrogenation.
Stearic acid is neither cis nor trans because it has no double bonds.
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Elaidic acid
C18H34O2
Unsaturated fatty acids become rancid relatively quickly.
To combat the instability of unsaturated fatty acids, manufacturers began
to "hydrogenate" them, a process that makes them more stable.
The result was a more solid and longer lasting form of vegetable oil, called
"partially hydrogenated" oil, in which a new type of fatty acid is formed.
This new type of fatty acid is called trans fatty acid.
Trans fatty acids turn out to increase total cholesterol levels
and LDL cholesterol levels, and to reduce HDL cholesterol levels.
In other words, trans fatty acids are detrimental to cardiac health.
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Wachenroder isolated β-carotene from carrots in 1831
giving the extracted crystals the name 'carotene'.
Ripe gac fruits
β-carotene
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Physical properties of alkenes (and alkynes) are very similar to the physical
properties of alkanes with the same number of carbons (and skeletal structure).
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Addition of hydrogen (hydrogenation) across
carbon-carbon double bond converts alkenes into alkanes.
CH3
CH3
H2C
CH
H2C
CH2
C
H2
C
H2C H CH2
H2C
C
H2
CH2
Additions of halogens (Cl2, Br2, I2, etc) also called halogenation:
Bromine and chlorine add readily to ethene to form 1,2-dibromoethane and
1,2-dichloroethane respectively. The reaction occurs even in the dark at room temperature.
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Markovnikov's Rule
In the addition of an unsymmetrical reagent such as
HCl, HBr and H2O to a double bond of an alkene,
the hydrogen atom adds to the carbon of the double bond
with the greatest number of hydrogen atoms.
H2C
H
C
Br
C
H2
CH3
+ HBr
CH3
C
H3C H C
H2
1-butene
H
C
H2C
CH3
C C
H2 H2
2-bromobutane
+ H2O
1-methylcyclopentene
Chemistry 21A
H2C
acid
H2
OH
C
CH3
C C
H2 H2
1-methylcyclopentanol
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Poly(ethene) (polythene or polyethylene)
an example of addition polymerisation
Temperature:
about 200°C
Pressure:
about 2000 atmospheres
Initiator:
a small amount of oxygen as an impurity
The number of molecules joining up is very variable, but is in the region of 2000 to 20000.
Low density poly(ethene) is used for familiar things like
plastic carrier bags and other similar low strength and flexible sheet materials.
High density poly(ethene) is used to make things like plastic milk bottles
and similar containers, washing up bowls, plastic pipes and so on.
Look for the letters HDPE near the recycling symbol.
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Poly(propene) (polypropylene): PP
It has uses in packaging - for example, in plastic film for shrink wrapping food.
There are also medical uses - for example,
in medical tubing and for medical bags and pouches.
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Poly(chloroethene) is commonly known by
the initials of its old name (polyvinyl chloride), PVC.
Poly(tetrafluoroethene): PTFE
You may have come across this under
the brand names of Teflon or Fluon.
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
“it takes alkynes to make a world”
Chemist humor
The chemical bonding in compounds such as
alkynes with triple bonds is explained by sp
hybridization.
In this model the 2s orbital mixes with only
one of the three p-orbitals resulting in two sp
orbitals and two remaining unchanged p
orbitals. The chemical bonding in acetylene
(ethyne) (C2H2) consists of sp–sp overlap
between the two carbon atoms forming a σ
bond and two additional π-bonds formed by
p–p overlap. Each carbon also bonds to
hydrogen in a sigma s–sp overlap at 180°
angles.
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
H C C H
HC CH
Acetylene is a colorless,
unpleasant-smelling gas (bp 28.1°C), which burns in air to
produce a very sooty flame.
In the presence of pure oxygen,
however, it burns at very high
temperatures (up to 2800°C), and
is used in welding and cutting
torches.
Chemistry 21A
Two pairs of p-orbitals
forming a π-bond
sp-sp s bond
In acetylene, the H-C≡C bond angles are 180°.
By virtue of this bond angle, alkynes tend to be rod-like.
C 2 H2
acetylene (ethyne)
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
two depictions
of propyne
the naturally-occurring
1-phenylhepta-1,3,5-heptatriyne
Capillin is an
antifungal agent.
the strained cycloheptyne
Pargyline is an antihypertensive agent, sold
under the trade names Eudatin® and Supirdyl®
IUPAC Nomenclature
1. alkane name - “ane” + “yne”
ethyne (acetylene)
Chemistry 21A
butynes
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
R-C≡C-R + H2 & Lindlar catalyst ——> cis R-CH=CH-R
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
AROMATIC COMPOUNDS
Discovery in 1825 by
Michael Faraday
In 1858, August Kekule proposed a rapid
oscillation (I & II) between the 3 C=C and the
3 alternating C-C of hexagonal benzene (C6H6).
Linus Pauling proposed
resonance theory in 1931
C6H 6
BENZENE
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
All the C-atoms in benzene are sp2-hybridized. Two sp2-hybrid orbitals of each
C-atom overlap with two sp2-hybrid orbital of two other C-atoms to form sigma
bonds. In this way there are six sigma bonds are formed between six C-atoms
which are 120o apart. Remaining six sp2-orbital of six C-atoms overlap with 1s
orbital of six H-atoms individually to form six sigma bonds. Since sigma bond
results from the overlap of above said planar orbital, all H and C atoms are in the
same plane and their generate a hexagonal ring of C-atoms.
Each C-atom in benzene also has an unhybrid 2pz-orbital containing one electron.
These 2pz-orbital are perpendicular to the plane of sigma bonds
Actually these 2pz-orbital produce a pi-molecular orbital containing six electrons.
One half of this pi-molecular orbital lies above the plane of hexagonal ring and
remaining half below the ring like a sandwich.
The overlap of these 2pz-orbital result in the formation of a fully delocalized
pi-bond, which extends all over the six C-atoms of benzene nucleus.
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
chemical formulas of benzene
π-electrons in benzene
Kekule
Pauling
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
heterocyclic
aromatic
compound
heterocyclic
aromatic
compound
naphthalene
Why is Trinitrotoluene (TNT) Explosive? Because nitrogen in the nitro
group (NO2) has a charge of +1, the nitro group has a very strong tendency
to withdraw (pull) electrons from the aromatic ring. Therefore, attaching
three nitro groups to a benzene ring leads to an extremely unstable or
explosive compound.
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
C6H5-
C6H5CH2-
phenylcyclohexane
OH
benzyl alcohol
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Benzene boils at 80°C - rather higher than other hydrocarbons of similar molecular
size (pentane and hexane, for example). This is presumably due to the ease with
which temporary dipoles can be set up involving the delocalized electrons.
Methylbenzene (toluene) boils at 111°C.
It is a bigger molecule and so the
van der Waals dispersion forces will be bigger.
You might have expected that methylbenzene's melting point would be higher than benzene's as well,
but it isn't - it is much lower! Benzene melts at 5.5°C; methylbenzene at -95°C.
Molecules must pack efficiently in the solid if they are to make best use of their intermolecular forces.
Benzene is a tidy, symmetrical molecule and packs very efficiently.
The methyl group sticking out in methylbenzene tends to disrupt the closeness of the packing.
If the molecules aren't as closely packed, the intermolecular forces
don't work as well and so the melting point falls.
The arenes (aromatic compounds) are insoluble in water.
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Benzene is resistant to addition reactions.
Adding something new to the ring would need you to use some of
the delocalized electrons to form bonds with whatever you are adding.
That results in a major loss of stability as the delocalization is broken.
Instead, benzene mainly undergoes substitution reactions –
replacing one or more of the hydrogen atoms by something new.
That leaves the delocalized electrons as they were.
Br
+
Chemistry 21A
Br2
+ HBr
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Polycyclic aromatic hydrocarbons (PAHs)
are chemical compounds that consist of
fused aromatic rings and do not contain
heteroatom or carry substituents.
PAHs occur in oil, coal, and tar deposits,
and are produced as byproducts of fuel
burning (whether fossil fuel or biomass).
As a pollutant, they are of concern because
some compounds have been identified as
carcinogenic, mutagenic, and teratogenic.
PAHs are also found in foods. Studies have
shown that most food intake of PAHs comes
from cereals, oils and fats. Smaller intakes come from vegetables and cooked meats.
The term carcinogen refers to any substance,
radionuclide or radiation that is
an agent directly involved in the promotion of
cancer or in the increase of its propagation
Chemistry 21A
mutagen is a physical or chemical
agent that changes the genetic material
teratology generally refers to disfiguring
birth defects or malformations
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
However, please, keep in mind that most
aromatic compounds
are beneficial (many medical drugs are aromatic)
and some even essential in our diet and nutrition (some amino acids, vitamins…)
phenylalanine
tryptophan
tyrosine
tyroxine
Alpha-tocopherol (Vitamin E)
Pyridoxine
(Vitamin B6)
Riboflavin (vitamin B2)
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
DNA A, C, G, T
RNA A, C, G, U
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Chemistry 21A
Dr. Dragan Marinkovic
UNSATURATED HYDROCARBONS
Chemistry 21A
Dr. Dragan Marinkovic