unsaturated hydrocarbons chemistry 21a dr. dragan marinkovic hydrocarbons saturatedunsaturated...

UNSATURATED HYDROCARBONS

Chemistry 21A Dr. Dragan Marinkovic

HYDROCARBONS

SATURATED UNSATURATED

ALKANES ALKENES ALKYNES

AROMATICS

H

H

H

H

H

H C C

H

HH

H

CC

HH CC

H

H

H

H

H

HC

C

CC

CC

RING WITH CONJUGATED DOUBLE BONDS

CONJUGATED DOUBLE BONDS

ISOLATED DOUBLE BONDS

PARAFFINS

CYCLOALKANES



ethene (ethylene) propene (propylene)

1-butene (1-butylene)chloroethene (chloroethylene)

vinyl chloride

cis-2-butene trans-2-butene



Muscalure, or cis-9-tricosene, is the sex pheromone of the female common

housefly (Musca domestica)

C23H46

cyclopropene

cycloheptene

cyclooctene

butadiene

cyclopentadiene

propan-1,2-diène



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



p-orbitals

s-orbitals

sp2-orbitals



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.

π-bond

Ethylene (ethene), showing the pi bond in green



Since sp2 hybrid orbitals are always in the same plane, the entire ethylene molecule is planar.

cis-2-butene trans-2-butene

Cis-/trans- isomerism are the consequence of the planarity of all atoms bonded to double-bonded (C=C) carbon atoms.



cyclopropene

cycloheptene

CH2

CH2

CH

CH2 CHCH2

CH2

All are cis

CH3

H H

CH3CH3

H CH3

H CH3

CH3 H

H

cis-2-butene trans-2-butene methylpropene



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.

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.

C18H34O2

C18H36O2



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.

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.

Elaidic acid C18H34O2


Wachenroder isolated β-carotene from carrots in 1831 giving the extracted crystals the name 'carotene'.

β-carotene


Ripe gac fruits



Physical properties of alkenes (and alkynes) are very similar to the physical properties of alkanes with the same number of carbons (and skeletal structure).



Addition of hydrogen (hydrogenation) across carbon-carbon double bond converts alkenes into alkanes.

CH2

CH2 CH2

CH2

CH

CH3

CH2

CH2 CH2

CH2

CH2

CH

CH3

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.



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.

CH2

CH

CH2

CH3 CH3

CH C

H2

CH3

Br

+ HBr

CH2

CH2

CH

CH2CH3

CH2

CH2

CH2

CH2CH3

OH

+ H2Oacid

1-butene 2-bromobutane

1-methylcyclopentene 1-methylcyclopentanol



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.

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.

Low density poly(ethene) is used for familiar things like plastic carrier bags and other similar low strength and flexible sheet materials.



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.

Poly(propene) (polypropylene): PP



Poly(chloroethene) is commonly known by the initials of its old name (polyvinyl chloride), PVC.

Poly(tetrafluoroethene): PTFEYou may have come across this under

the brand names of Teflon or Fluon.



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.

“it takes alkynes to make a world”Chemist humor



acetylene (ethyne)

CH CHHH C C

In acetylene, the H-C≡C bond angles are 180°. By virtue of this bond angle, alkynes tend to be rod-like.

sp-sp s bond

Two pairs of p-orbitals

forming a π-bond

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.

C2H2



two depictions of propyne

the naturally-occurring 1-phenylhepta-1,3,5-heptatriyne the strained cycloheptyne

Capillin is an antifungal agent. Pargyline is an antihypertensive agent, sold

under the trade names Eudatin® and Supirdyl®

IUPAC Nomenclature 1. alkane name - “ane” + “yne” ethyne (acetylene) butynes



R-C≡C-R + H2 & Lindlar catalyst ——> cis R-CH=CH-R



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).

C6H6

Linus Pauling proposed resonance theory in 1931

BENZENE

AROMATIC COMPOUNDS



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

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.

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.



π-electrons in benzene

chemical formulas of benzene

Kekule

Pauling



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.

heterocyclic aromatic compound

heterocyclic aromatic compound

naphthalene



C6H5-

C6H5CH2- OH

phenylcyclohexane

benzyl alcohol



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.



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

+ Br2 + HBr



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

mutagen is a physical or chemical agent that changes the genetic material

teratology generally refers to disfiguring birth defects or malformations

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.


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

Pyridoxine (Vitamin B6)

Riboflavin (vitamin B2)

Alpha-tocopherol (Vitamin E)




DNA A, C, G, T

RNA A, C, G, U

unsaturated hydrocarbons chemistry 21a dr. dragan marinkovic hydrocarbons saturatedunsaturated...

Documents

cis unsaturated fatty

trans unsaturated fatty

butene slide

dragan marinkovic alkanerch

dragan marinkovic muscalure

dragan marinkovic elaidic

c carbon atoms

butene trans