5: Alkenes Flashcards
Alkenes
hydrocarbons with a carbon-carbon double bond.
Called unsaturated hydrocarbons cuz they have < the max # of H.
Dregree of unsaturation
the # of π bonds or rings in a molecule
Degree of unsaturation formula
2(n)+2-#H
2
n=#carbons
Alkane general molec formula
acyclic: CnH2n+2
cyclic: CnH2n
Alkene general molec formula
acyclic: CnH2n
cylcic: CnH2n-2
alkene naming
the suffix is “ene” replacing the -ane.
since the double bond is the functional group of an alkene.
Cyclopentene
Longest chain w/ functional group is given lowest #
Ex: CH3CH=CHCH2CH2CH3
2-hexene
stereoisomers def
isomers that differ in the way their attoms are arranged in space
stereo isomers named using
- cis:* meaning same (same plane)
- trans: *meaning different (diff plane)
compound with two double bonds
-diene
cyclic molecules
a double bond in a cyclic is always belween C 1 &2
trans-1,2-dichloroethene
Naming practice
(E)-3-chloro-4-methyl-2-pentene
vinylic carbons
the sp2 carbons of an alkene
allylic carbons
attached to an vinylic carbon, is also sp3
E/Z system
for alkenes that do not have a H attached to each of the sp2 carbons
IUPAC
Naming with E/Z
- break by DB & determine priotities of groups bonded to each of carbons. (priorities depend on atomic #)
- Z higher priotities on same side
- E higher priorities on opposite sides
“Z” isomer
“zee zame zide” higher priotities on same side
“E” isomer
high-priority groups on opposite sides
if atom is DB
treat as if it were single bonded to two atoms
if atom is triple bonded
treat as if 3 single atoms are there
priority with isotopes
the isotope with higher mass number has higher priority
electrophile
electron deficient atom
“electron loving”
spot: inc octet, positive charge, or partial positive, acid
nucleophile
electron rich.
“likes the nucleus”
Has a pair of electrons it can share.
Spot: complete octet, base
neucleophiles react with electrophiles
π bonds are weakest in an alkene. break first ( befire σ bonds)
electrophilic adition reactions
has the addition of an electrophile
kinetics
describes the rate of chemical rxns
Lower energy means
more stable species
thermodynamics
says how much reactants and products are present in a rxn
Equilirium constant
stable compound has greater concentration
Keq>1
Products are favored. More stable
Gibb’s free energy
net sum of all energy in an eqtn
exergonic
-ΔG products are favored, energy is given off
endergonic
ΔG, reactants are favored energy is consumed
Le Châtelier’s principle
if a system is disturbed, it will adjust its concentrations to maintain its eq constant.
enthalpy ΔH
thermal energy used/given off in an equation
heat realeashed when bonds formed
heat consumed when bonds broken
(heat requ to break bonds)-(Heat released by forming bonds)
exotherminc
-ΔH bonds formed are stronger
endotherminc
ΔH bonds formed are weaker than bonds broken
Entropy
measure of freedom of motion in a system
nature’s disorder or randomness(favored)
+ΔS
greater freedom of motion
Disorder :)
-ΔS
less freedom of motion
trying to bring order :(
bond dissociation
energy required to break a bond
Listed values used to determine ΔH
energy diagram
Kinetics
determines how fast a rxn will occur and factors affecting it
