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