chapter 13 Unsaturated hydrocarbons

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alkene

an acyclic unsaturated hydrocarbon that contains one or more C-C double bonds
- Molecular formula = CnH₂n (2 less than alkane)
- Geometry = trigonal planar

2 simplest alkenes

1. Ethene C₂H₄ --> CH₂=CH₂ (flat, 120°) Common name is ETHYLENE
2. Propene C₃H₆ ---> CH₂=CH-CH₃ Common name is PROPYLENE

cycloalkene

a cyclic unsaturated hydrocarbon that contains one or more C-C double bonds within the ring system
- Molecular formula = CnH₂n-₂ (4 less than alkane)
- simplest = cyclopropene C₃H₄

alkenes substituents are called

alkenyl groups

most frequent alkenyl groups (3) MEP

1. Methylidene, aka methylene (one-carbon) CH₂=
2. Ethenyl, aka vinyl (two-carbon) CH₂=CH-
3. 2-propenyl, aka allyl (three-carbon) CH₂=CH-CH₂-

alkenyl group

is a noncyclic hydrocarbon substituent in which a C-C double bond is present

constitutional isomers - 2 types

1. positional
2. skeletal

positional isomer

constitutional isomers with the same C-chain arrangement but different hydrogen atom arrangements as the result of differing locations of the functional group (where the functional group (multiple bond) is located)

skeletal isomer

constitutional isomers that have different C-chain arrangements as well as different hydrogen atom arrangements
Note: all alkanes isomers are skeletal b/c they don't have functional groups

unsaturated hydrocarbon

a hydrocarbon in which one or more C-C multiple bonds are present
-physical properties similar to saturated
-chemical properties are distinct
-more reactive than saturated b/c of C-C multiple bonds

functional group

the part of an organic molecule where most its chemical reactions occur. C-C multiple bonds

3 types of functional groups

1. alkenes = DB
2. alkynes = TB
3. aromatic hydrocarbons

isomer

the same molecular formula but different structural formulas

Cis-Trans isomers

exists when each carbon atom in a DB contains two different groups attached to it.
- if one of the carbons has two identical groups then it cannot be cis-trans isomer

Cis isomer

has two similar groups on the same side of DB

Trans isomer

has two similar groups on opposite sides of the DB

pheromones

a compound used by insects (and some animals) to transmit a message to other members of the same species
-depends if the DB present are in a cis or trans arrangement

pheromone steps (3)

1. identify specific organic compound
2. synthesize the compound
3. use it to trap male insects

terpene

an organic compound whose carbon skeleton is composed of 2 or more 5-carbon isoprene structural units. 22,000 found. carbon atoms in multiples of 5

physical properties of alkenes & cycloalkenes

1. similar to alkanes
2. BP & MP are usually lower than alkanes w/same # of Carbons
3. 2-4 carbons = gas at room temp
4. unsubstituted with 5-17 carbons are liquid
5. >17 carbons are solid
6. insoluble in water
7. soluble w/non-polar solvents

combustion of alkenes

1. very flammable
2. products are CO₂ & H₂O

addition reaction

a reaction in which atoms or groups of atoms are added to each carbon atom of a C-C multiple bond in a hydrocarbon or hydrocarbon derivative

2 kinds of addition reaction

1. symmetrical
2. unsymmetrical

symmetrical addition reaction

an addition reaction in which identical atoms (or groups of atoms) are added to each carbon atom in a C-C multiple bond.

2 kinds of symmetrical addition reaction

1. hydrogenation
2. halogenation

symmetrical addition reaction: hydrogenation

an addition reaction in which H₂ is incorporated into molecules of an organic compound. Added to each carbon in the DB
- catalyst = usually Ni or Pt

symmetrical addition reaction: halogenation

an addition reaction in which a halogen in incorporated into molecules of an organic compound. Added to each carbon in the DB
- no catalyst

unsymmetrical addition reaction

an addition reaction in which different atoms (or groups of atoms) are added to each carbon atom in a C-C multiple bond

2 kinds of unsymmetrical addition reaction

1. hydrohalogenation
2. hydration

unsymmetrical addition reaction: hydrohalogenation

an addition reaction in which a hydrogen halide (HCl, HBr, or HI) is incorporated into molecules of an organic compound. one carbon gets halogen, other carbon gets hydrogen.
- no catalyst

unsymmetrical addition reaction: hydration

an addition reaction in which H₂O is incorporated into molecules of an organic compound.
-requires sulfuric acid H₂SO₄
-In symmetrical alkenes, only one product results

markovnikov's rule

when a unsymmetrical molecule of the form HQ adds to an unsymmetrical alkene, the hydrogen atom from the HQ becomes attached to the unsaturated carbon atom that already has the most hydrogens

alkenyl group: Methylidene

one carbon aka: methylene
CH₂

alkenyl group: ethenyl

2 carbon aka vinyl
CH₂=CH-

alkenyl group: 2-propenyl

3-carbon, aka allyl
CH₂=CH-CH₂-

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