Alkenes

reactivity of alkene

-More reactive due to Pie-bond presence, as they are more exposed than electrons on sigma bond. -So pie bond breaks easily and undergoes reactions relatively easily

4 isomers of C4H8

1-butene cis 2 butene trans 2 butene 2-methyl-propene

3 types of alkenes

1. Terminal- has a double bond at the end of the carbon chain 2., internal- has at least one carbon atom bonded to each end of the double bond 4. Cyclo-contains a double bond in a ring

bonding

1st bond is a sigma bond. The 2nd bond is a pi bond with areas of electron density above and below the plane of the molecule. The weakness of the pi bond is why alkenes are more reactive than alkanes. The bond is localised as the pi bond electrons do not move away from the 2 C atoms in the double bond

2-methylpropene + H-O-H yields

2-methyl-2-propanol

benzene bonding cont

6 carbons sharing 6 sigma electrons equally above and below the plane of the ring

what is a carbocation

A carbon atom with 3 bonds and a positive charge

Acetylene Shape

A linear molecule e bond angles of 180

Ex of addition reaction

A reaction of an alkene such as ethylene with H2 to yield an alkane ethane

Elimination reaction

A single reactant splits into 2 or more products a saturated reactant yields an unsaturated product by losing grps from 2 adjacent atoms

Addition reaction

A substance x-y adds 2 the multiple bond of an unsaturated reactant 2 yield a saturated product that has only single bonds alkene yields alkane

Halogenation

Addition of Cl2 or Br2 to a multiple bond to give a dihalide product Remove db and connect Cls to each carbon

Hydrohalogenation

Addition of HCl or HBr to an multiple bond to give an alkyl halide product Remove db and place Br connected to C

Hydration

Addition of water to a multiple bond to give an alcohol product

Cis trans isomerism is possible when

An alkene has 2 different substituent groups on each of its ends

1-hexene

C6H12

structural isomers

C8

Aromatic

Class of compounds that contain benzene like rings with alternating single and double bonds

Ex of rearrangement reaction

Conversion of cis-2-butene into its isomer trans-2-butene by trtment w an acid catalyst

determing the major product

Determines the major and minor product of an addition reaction involving an unsymmetrical alkene. Rich gets richer.

cycloalkene

Double bond contained in a ring

Ex of elimination reaction

Ethanol eliminates to give water and an alkene when treated w acid catalyst

Ethylene Shape

Flat molecule w bond angles of 120

formation of Pi Bond

Formed from the overlap of an electron in adjacent P orbitals. Each C atom donates one electron to both the sigma bond and P-orbitals above and below

hydrohalogenation of alkenes

HBr yields alkyl bromide HCl yields alkyl chlorides

internal alkene

Has at least one carbon atom bonded to each end of the double bond

terminal alkene

Has double bond at the end of the carbon chain

isomers of C6H14

Isomers of C6H14 include the following: 1) n-hexane 2) 2-methylpentane 3) 3-methylpentane 4) 2,3-dimethylbutane 5) 2,2-dimethylbutane All have the same formula, but they differ in their carbon framework and in the number and type of atoms bonded to one another.

Saturated (Alkanes)

Molecule in which ea carbon atom has the maximum number of single bonds possible(4)

Unsarurated (Alkenes and Alkynes)

Molecule that contains one or more carbon-carbon multiple bonds

Properties of alkenes

Non polar insoluble in water soluble in non polar solvents less dense than water flammable nontoxic multiple bonds r chemically reactive

Rearrangement reaction

Occurs when bonds and atoms in the reactant r reorganized 2 yield a single product that is an isomer of the reactant

sigma bond type of bond

Strong covalent bond found in a carbon-carbon double bond.

Ethane shape

Tetrahedral shape w bond angles of 109.5

Hydrogenation

The addition of H2 to a multiple bond to give a saturated product Alkenes and alkynes react with metal catalyst 2 yield alkane product

bond enthalpy

The pi bond is weaker than the sigma bond (pi bond = 264kjmol-1, sigma bond = 346kjmol-1)

Resonance

The true structure of a molecule is an average among 2 or more conventional Lewis structures that differ only in placement of double bonds

Properties of Alkenes

Weak London dispersion forces those w 1-4 carbon atoms r gases at rm temp and boiling pts inc w size of molecules

pi bond type of bond

Weak covalent bond with just one electron. Found in a carbon-carbon double bond, where is it found in pairs.

2-methyl-pentane 4 structural isomers

a) hexane c) 3-methylpentane d) 2,2-dimethylbutane e) 2,3-dimethylbutane

elimination alkene

add double bond and H2O to form alkene

substitution alkene

adding 2 Hs and Cl

halogenation adds_____ and forms________ its solvent is______

adding: Cl2 or br2 solvent: trichloromethane forms: dihalogenated compound

hydration adds_________and forms_______ its catalyst is____________

adding: H2O catalyst: H2SO4 forms: alcohol

hydrohalogenation adds________ and forms____________

adding: hydrogen halide/HX forms: Halo(alkene)

sigma electrons

alkenes much more reactive than alkanes due to greater availability of the sigma electrons(not attratced as strongly to the nuclei since the electrons r not bw the 2 nuclei but above and below the plane

bonding in benzene

all 6 carbon atoms are sp2 hybridized : orbitals form a bonds with 2 other C and 1 H

benzene p orbitals

all 6 unhybridized p orbitals (one from each C) form a delocalized sigma bond

unsymmetrical alkene

an alkene in which 1 of the double-bond carbons has more hydrogens than the other

symmetrical alkene

an alkene in which both of the double bonded carbons has equal hydrogens

pi bond

any 2nd or 3rd bond made w any other atom

testing for unsaturation with bromine

disappearance of the bromine color when its added to 1-hexene (C6H14) indicates presence of double bond

unsaturated compound

double and triple bonds

sigma bond

electron density above and below plane of 2 nuclei

a bond

electron density bw the 2 nuclei

halogenation of ethylene

ethylene + Cl2

sigma bond

first bond made w any other atom

is it an aromatic compound

flat and delocalized electrons must have 4n+2 pie electrons odd # of double bonds=aromatic

minor product

halogen or the OH bonded to carbon atom with the most number of carbon atoms bonded to it

markovnikovs rule

in addition of HX to an alkene, the major product arises from the H attaching to the double bond carbon that has the larger number of H atoms directly attached to it and the X attaching to the carbon that has the smaller number of H atoms attached

carbocations

intermediates that form during the reaction

2-methylpropene+HBr

major product-2-bromo-2-methylpropane

2-pentene

not a symmetrically substituted alkene

isomers for pentane

pentane isopentane neopentane

rearrangement alkene

regarding cis and trans

saturated compound

single bonds

catalyst

speeds up reaction with being consumed lowers energy of activation E by providing different mechanism(diff pathway from reactants to products) (E=energy needed to break old bonds before new bonds can form-endothermic)

benzene sulfonic acid

sulfonication

hindered rotation

the 2p orbitals forming the sigma bond must remain parallel to each other-rotation around the a bond would destroy the orbital overlap and break the sigma bond

major product

the hydrogen is added to carbon atom with least number of carbon atoms bonded to it

phenol C7H8O isomers

toline anisole aniline benzaldehyde benzoic acid

reaction of HBr and alkenes

● Change in functional group: ● alkene --> halogenoalkane ● Reagent: HCl or HBr ● Conditions: Room temperature ● Mechanism: Electrophilic Addition ● Type of reagent: Electrophile, Hδ+ ● Type of Bond Fission: Heterolytic

hydrogenation adds____ and its catalyst is ____

● Change in functional group: alkene --> alkane ● Reagent: hydrogen ● Conditions: Nickel Catalyst ● Type of reaction: Addition/Reduction

reaction with Br2 or Cl2 and alkene

● Change in functional group: alkene --> dihalogenoalkane ● Reagent: Bromine (dissolved in organic solvent) ● Conditions: Room temperature (not in UV light) ● Mechanism: Electrophilic Addition ● Type of reagent: Electrophile, Brδ+ ● Type of Bond Fission: Heterolytic