ALKENES & ALKYNES Flashcards
ALKYNES
C≡C
TERMINAL ALKYNE
C≡C at END of chain
INTERNAL ALKYNE
C≡C in chain (not end)
Compare reactivity of alkenes & alkynes
ALKENES MORE REACTIVE
What bond types is a C≡C composed of?
1 sigma, 2 pi
alkynes undergo which mechanism
ELECTROPHILIC ADDITION
Which tautomer predominates in solution? Why?
KETO form - MORE STABLE
ENOL formed first.
What is a regioselective reaction?
major product formed via most stable carbocation.
PREFERENTIAL FORMATION OF ONE CONSTITUTIONAL ISOMER.
ALKENE -> HALOALKANE
ELECTROPHILIC ADDITION
HYDROHALOGENATION
H-X + ALKENE
Describe the products of hydrohalogenation
ASSYMETRIC alkenes can form >1 product
SYMMETIC alkenes form 1 product.
CARBOCATION MEDIATED
ALKENES -> ALCOHOLS
ACID-CATALYSED (H-OH)
ALKENE + H2O -> ALCOHOL
CARBOCATION MEDIATED
ALKENES -> ALKANES
Markovnikov
HYDROGENATION (H-H)
METAL CATALYST
Pt, Pd, Ni
State metal catalysts which can be used for hydrogenation
Pt, Pd, Ni
ALKENES -> ALKANES
Anti-Markovnikov
H-Br in presence of PEROXIDES.
Free radical formation
HETEROLYTIC FISSION.
HOMOLYTIC addition involves…
RADICALS
HETEROLYTIC addition involves…
CATIONS
Describe Markovnikovs rule
Electrophiles add to form the most stable intermediate in ELECTROPHILIC ADDITION.
Which HALOGEN has the correct energy for an Anti-Markovnikov Addition
H-Br
ALKENE -> VICINAL DIHALOALKANE (DIHALIDE)
HALOGENATION (X-X)
STEREOSPECIFIC
ALKENE -> adihalogenated alkane
ALKYNE -> TETRAHALOGENATED alkane
Order the stability of carbocations from MOST to LEAST
Tertiary -> Primary
State the limitation of Markovnikovs rule
VALID only for ADDITION reactions where electrophile is H+
