Functional Group Chemistry 2 Flashcards
Describe alkanes
Saturated = single bonds = sigma
CnH2n+2
pKa > 50
What are the properties of alkanes?
Poorly reactive with ionic or polar substances
Inert to acids + bases
Virtually insoluble to H2O
What happens to boiling point as size of alkanes increase?
Increase
What are alkanes used for?
Fuels
Describe intermolecular forces of alkanes
Weak = no difference in electronegativity = no dipoles
Describe alkenes
Unsaturated = pi bonds
Double bond = slightly polar
CnH2n
What is reactivity controlled by in alkenes?
How e- rich the double bond is = act as nucleophile
What does it mean the pi bond in alkenes is polarizable?
= instantaneous dipole-dipole interactions occur
What do the conversion of alkene isomers require?
Breaking of pi bond between 2x sp2 carbons
How do you get from alkene cis to trans?
180 degrees
UV light
What is cis?
Same side
What is trans?
Opposite
What happens when C=C is broken to C-C?
ISOMERS
C=C reformed to form more stable orbitals
What is the preparation methods for alkenes?
Cracking
Elimination reactions of halides/alcohols
What can alkenes form?
Haloalkanes Alcohols Vicinal dihaloalkanes Alkanes Polymers
What is addition reactions via for alkenes?
Electrophilic addition
Where does e- move in alkenes?
From double bond to electrophilic centre
What can addition reactions be?
Homolytic (involves radicals)
Heterolytic (involves cations)
Describe reactivity of C=C
Pi e- attack E+ (heterolytic) or radical intermediate (homolytic)
Nu- adds to carbocation/radical
Describe addition of halogens to alkenes
Cl2, Br2 + I2 add to C=C to form vicinal dihalide
Anti or trans addition = stereospecific reaction
Describe addition of bromine to alkenes
Red/brown colour goes colourless upon reaction
Br- = Nu-
Describe addition of H-X to alkenes
Symmetrical alkene = 1 product
Unsymmetrical = 2 different products
Describe anti-Markovnikov addition to alkenes
Peroxides present = HBr adds to alkenes to form “Anti-Markovnikov” product through radical mechanism
Only HBr has right bond energy
Describe anti-Markovnikov addition to alkenes stages
Initiation + propagation = Br2 adds to sterically least hindered C
Radical cleaves HBr in 2nd propagation
= radical chain
Termination = contamination
Describe hydrogenation in alkenes
Form alkane
Syn or Cis addition
Reaction = stereospecific
Catalyst required = Pt, Pd or Ni
Describe alkynes
Unsaturated Triple bonds Reactivity dominated by reactive e- rich triple bond CnH2n-2 pKa = 44
What are the properties of alkynes?
Virtually insoluble to H2O
Stronger Van Der Waals
Internal alkenes/alkynes have higher boiling points than terminal
Describe electronegativity of orbitals
sp > sp2> sp3
sp = most
sp3 = least
What happens to acidity as s-orbital character increases?
Increases
Describe alkyne reactivity
Completely burn in O2
What reactions do alkyne undergo?
H-X addition With/without peroxides X-X addition (Br2, Cl2) Hydrogenation H-OH (hydration) Alkylation of terminal alkynes
Describe addition of HX to alkynes
Follows Markovnikov rule
Vinylic carbocations in 1st step
Triple bond compose of sigma bond + 2x pi bonds
Pi bond broken = new sigma bonds formed
2nd addition
What are the alkyne addition reaction?
Halogenation = same as alkenes Anti-Markovnikov = needs peroxide
Describe addition of H2O to alkynes
Same as alkenes
Acid catalysed
