Chem 12 Chapter 2 Unsaturated Hydrocarbons

Chemical reactions of alkenes: Symmetrical Addition Reactants Halogenation reaction

In alkene halogenation, a halogen atom is added to each carbon atoms of a double bond (addition of Halogen) - no catalyst required

Chemical reactions of alkenes: Symmetrical Addition Reactants Hydrogenation reaction-

In alkene hydrogenation, a hydrogen ato is added to each carbon atom of a double bond (addition of H2) - catalyst is usually Ni or Pt

Terpenes example

Isorpene (2-methyl-1,3-butadiene) is a five carbon diene show picture in slide

Copolymers examples

Saran wrap -- chloroethene ( vinyl chloride) and 1,1-dichloroethene Styrene-butadiene rubber --1,3 butadiene and styrene in a 3:1 ratio

Cyclopropene (C3H4) is the

simplest cyloalkane - a three membered carbon ring system with one double bond

Isomerism and alkynes

*Cis- trans isomerism is not possible* due to the linearity 180 angles about an alkynes triple bond *Constitutional isomers are possible* - relative to the carbon chain (skeletal isomers) and to the position of the triple bond (positional isomers)

Unsaturated Hydrocarbons : Functional groups is subdivided into 3 groups

- Alkenes - Alkynes -Aromatic hydrocarbons

Characteristics of Alkenes

-Acyclic( not circular ) unsaturated hydrocarbons aht contain one or more carbon-carbon double bonds - functional group - C=C group - Names end with ene versus and --ene signifies the presence of a double bond

Properties of Alkynes

-similar to those of alkenes and alkanes -insoluble in water but soluble in organic solvents - densities less than that of water -boiling points increase with molecular mass -low molecular-mass alkynes are gases at room temperature * the bigger they are the higher their boiling point

Unsaturated Hydrocarbons: Functional Group

-structural feature of an organic molecule that is directly invovled in most of its chemical reactions -carbon- carbon double/triple bonds are the functional groups in unsaturated hydrocarbons

Nomenature: Alkene IUPAC rules

1. replace the alkane suffix -ane with the suffix -ene 2. Select as the parent carbon chain the longest chain of carbon atoms that contains both carbon atoms of the double bond 3. Number the parent chain beginning at the end nearest to the double bond 4. Give the position of the double bond in the chain as a single #, which is the lower-numbered carbon atom participating in the double bond

Chemical Reactions of Alkenes: Symmetrical Addition Reactions there are two

2 idential- either an H or Halogens Hydrogenation reaction Halogenation reaction

Nonmenature :Alkene IUPAC rules continued

5. use the suffixes -diene, -triene, -tetrene, - and so on when more than one double bond is present in the molecule 6. A number is not needed to late the double bond in unsubstituted cycloalkenes with only one double bond because that bond is assumed to be between carbons 1 and 2 7. In sunstituted cycloalkanes with only one double bond, the double-bonded carbon atoms are numbered 1 and 2 in the direction (clockwise or counterclockwise) that gives the first-encountered substituent the lower number 8. In cycloalkanes with more than one double bond within the rind, assign one double the numbers 1 and 2 and the other double bonds the lowest numbers possible

Naturally occurring Alkenes: Pheromones

A compound secreted or excreted by insects(and some animals and plants) the triggers a response in other members of the same species

Chemical Reaction of Alkenes: Chemical properties

Alkenes are very flammable -combustin products are carbon dioxide and water - Alkene + O2 --> CO2 + H2O

Fused ring aromatic hydrocarbons

Aromatic hydrocarbons whose structures contain two or more rings fused together

Alkynes examples

C2H2 C3H4 -if I can see the same when flipped its not an isomer

Cis- trans isomerism in alkenes:

Cis- trans isomerism in alkenes results from the structural rigidly associated with C=C bonds - rotation about C=C or (c triple bonds) are not possible

Alkenes General Formula

CnH2n

Cycloalkenes general molecular formula

CnH2n-2 -remove thwo H's within the cycle to form a double bond

Characteristics of Cycloalkenes

Cyclic(circular) unsaturated hydrocarbons with one or more carbon-carbon bonds within the ring system Those with more than one double bond are relatively common

Nomenature: Alkene Common Names (Non-IUPAC names) common names are used mostly for compounds Two most common

Ethylene- (IUPAC name- ethene) - CH2 = CH2 Propylene (IUPAC name-Propene) -CH2= CH-CH3

Halogen list

F2, Cl2, Br2, I2

Nomenclature: Alkenes as substituents Most frequently encountered alkenyl groups

Mentylidene (one-carbon) -common name-Methylene Ethenyl (two-carbon) -common name- Vinyl 2-propenyl (three-carbon) -common name Aliyl

3 need to be aware of:

Naphthalene Anthracene Phenanthracene add picture from last slide

Natural occurring Alkenes: Terpenes

Organic compounds whose carbon skeleton comprises two or more 5 carbon isoprene structural units

Physical properties of Alkenes and Cycloalkenes

Physical properties are similar to those of alkanes melting point of an alkene is usually lower than that of an alkane with same number of carbon atoms alkenes with 2 to 4 carbon atoms are gases at room temperature unsubstituted alkenes with 5 to 17 carbon atoms are liquids alkene with more than 17 carbons atoms are solids

Polymerization of Alkenes: Addition polymers

Polymers cannot be accurately represented by an exact formula -length of carbon chains vary with each polymer molecule - the notation used is independent of carbon-chain length add picture from slide 30

Ethene Methane

a flat molecule with bond angles of 120 a tetrahedral with bond angles of 105 add slide picture

Unsaturated Hydrocarbons

a hydrocarbon with *one or more carbon-carbon multiple bonds*

Polymerization of Alkenes: Addition Polymers Polymers-

a large molecule former by the repetitive bonding together of many smaller molecules

Nomenclature: Alkenes as Substituents Alkenyl group:

a noncyclic hydrocarbon substituent in which a carbon double bond is present

Addition polymer

a polymer in which monomers simply "add together" with no other products formed besides the polymer -it is similar to the addition reactions described previously except that there is no reactant other than the alkene or sunstitued alkenes

Chemical Reaction of Alkenes: Chemical properties Addition reaction

a reactin in which atoms or group of atoms are added to each carbon atom of a carbon-carbon multiple bond in a hydrocarbon or hydrocarbon dericative

Preparation of Alkenes: Dehydration reaction

a reaction characterized by the loss of a hydrogen atom from each of two adjacent carbon atoms, forming a carbon-carbon double bond.

What is the difference between alkene skeletal isomers and positional isomers?

add picture

Two of the simplest alkenes are ethene and propene

add picture of the two

Many Pheromones have

alkene structures -arrangement of double bonds (cis or trans) influences the biological activity of alkene-type pheromones

Alkynes-

an acyclic ( noncircular) unsaturated hydrocarbon (one or more mulitple carbon-carbon bonds) that contains one or more carbon-carbon triple bonds

Unsaturated Hydro carbons physical properties Unsaturated Hydrocarbons chemical properties

are similar to those of saturated hydrocarbons are distinct, chemical more reactive than saturated hydrocarbons

which has a higher melting point of butane or butene?

butane

Reactivity of unsaturated Hydrocarbons is due to

carbon-carbon multiple bonds -unsaturated hydrocarbons are more reactive

Constiutional Isomerism in Alkenes: skeletal isomers

constitutional isomers that possess different carbon-atom arrangements and that contain identical functional groups if functional groups are present

Constitutional Isomerism in Alkenes: Positional Isomers-

constitutional isomers that possess the same carbon-atom arrangement and that have differing locations for functional groups present (linked together in a line) add picture like slide 15

Alkenes

contain one or more carbon-carbon double bonds C=C

Alkynes

contain one or more carbon-carbon triple bonds

Aromatic hydrocarbons

exhibit a special type of "delocalized" bonding involving a six members carbon ring.

Addition polymer example

formation of polyethylene

Properties of and sources for *Aromatic hydrocarbons*

insoluble in water soluble in non-polar solvents less dense than water benzene is a colorless, flammable liquid that burns with sooty petroleum is the primary source of aromatic hydrocarbons

Alkynes functional group:

is a C to C triple bond group names end with suffix -yne the general formula is CnH2n-2

Cis and trans isomers are

isomers that exist when each of the two carbons of the double bond has two different groups attached to it

Overall unsaturated hydrocarbons are

more reactive have same physical property as SH's similar naming as SH's chemical properties are distinct

Preparation of Alkenes:

more reactive than alkanes

Nomenclature: Naming Benzene derivatives

name of the substituent is used as a prefix to the name benzene numbers of non numerical prefixes are used in the presence of more than one substituent -ortho 1,2 disubstitution -meta 1,3 disubstitution -para 1,4 disubstitution ( 3 substituents)

Terpene are widely disturbuted in isopene is the backbone of

nature more than 22,000 terpenes are found in biological systems and they are responsible for the characteristic ordors of many trees and plant fragrances terpenes

Polymerization of Alkenes: Addition Copolymers Copolymers-

polymers in which two different monomers are present

Aromatic Hydrocarbons: Bonding in Hydrocarbons Benzene

possesses a six-membered carbon ring represented using one of the following structures -*every other line has a double bond* picture 1 Equivalent nature of C-C bonds is aptly described using an average of the two structure - an alternative that uses a single stucture is picture 2

Line- Angle structural formulas for Alkenes and Cycloakenes: Diene-

represents more than one double bond is added to the end of then name when there 2 double bonds with alkenes example penta*diene* add picture of slides 13and 14

Preparation of Alkenes: Alkenes are not easily formed from alkanes- Easier alkene-produceing methods exist-

special catalysts and temperature of 500c requirred Dehydration of alchol- loss of water add little yellow boxed drawling if have time

Nomenclature for alkynes

the rules for naming alkynes are identical to those used to name alkenes, except the ending -yne is used instead of -ene * the tripple bond needs to have the lowest #

Pheromones example

the sexual attractant of the female silkworm is a 16-carbon alkene derivative containing an -OH group

alkene Cis-isomer

the two groups are located not the same side of the double bond

alkene trans-isomer

the two groups are located on the opposite sides of the double bond

Constitutional Isomerism in Alkenes: Alkene vs alkane

there are more alkene isomers possible for a given number of carbon atoms them there are alkane isomers

Chemical reactions of *Aromatic hydrocarbons*

they do not readily undergo the addition reactions characteristic of other unsaturated hydrocarbons Benzene undergoes substitution reactions Important substitution reactions are Alkylation Halogenation

Chemical Reactions of Alkenes: Unsymmetrical Addition Reactions Maokovnikov's rules

when an unsymmetrical molecule of the form of Hq reacts with an unsymmetrical alkenes, the hydrogen atom from the HQ becomes attached to the unsaturated carbon atom that already has the most hydrogen atoms

Polymerization of Alkenes: Butadiene- Based addition polymers

when dienes are used as monomers in addition polymerization reactions, the resulting polymers contain double bonds - double bonds are still unsaturated They are more flexible than ethane-based saturated polymers