Chapter 13 - Alkenes Flashcards
(25 cards)
what are alkenes?
unsaturated hydrocarbons
what is the general formula for alkanes?
CnH2n
What type of bonds are formed in alkenes?
ó bond and pi bond
how is a pi bond formed?
by the sideways overlap of two orbitals
can the double bond rotate?
no
what is the shape around each carbon atom in an alkene?
trigonal planar
what is the bond angle around a carbon in an alkene?
120
what is stereoisomerism?
having the same structural formula but a different arrangement of the atoms in space
what are the requirements for E/Z isomerism?
- C to C double bond
- different groups attached to each carbon atom of the double bond
what is the requirement for cis-trans isomerism?
one of the attached groups on each carbon of the double bond must be hydrogen
which isomer has the hydrogens on the same side?
cis
is a cis isomer a z or e isomer?
z
is a trans isomer a z or e isomer?
e
what is the Cahn - Ingold - Prelog nomenclature rule?
the atoms attached to each double bonded carbon are given a higher priority if they have higher atomic numbers
if the groups of higher priority are on the same side, what isomer is it?
Z
if the groups of higher priority are on the diagonal side, what isomer is it?
E
why are alkenes more reactive than alkanes?
the pi electrons are more exposed than the electrons in the ó bond
what are the four addition reactions of alkenes?
hydrogenation
halogenation
with hydrogen halides
hydration
what is the hydrogenation of alkenes?
when an alkene is mixed with hydrogen and passed over a nickel catalyst at 423K, an alkane is formed
what is the halogenation of alkenes?
alkenes react with chlorine or bromine at room temperature
what happens in the reaction with alkenes and hydrogen halides?
alkenes react with gaseous hydrogen halides at room temperature to form haloalkanes
what is the hydration of alkenes?
when alkenes react with steam in the presence of a phosphoric acid catalyst to form an alcohol
what is electrophilic addition?
the mechanism of alkenes in addition reactions to form saturated compounds
what is an electrophile?
an atom or group of atoms that is attracted to an electron rich centre and accepts an electron pair
