13 properties of alkenes Flashcards
(28 cards)
What 2 types of bond does a C to C double bond consist of
1 sigma bond and 1 pie bond
What orbital are the E- in carbon atoms in and what shape are they
p orbital, dumbell shaped
A single pie bond consists of…
…Both overlaps of the p orbitals either side of the sigma bond, like a hot dog in a roll
What affect does the presence of a pie bond have on rotation
Restricts rotation around C to C double bond
Name of 3d shape around C to C double bond and bond angle
trigonal planar, 120°
Stereoisomerism + 2 types?
Have same structural formula but diff arrangement of atoms in 3d space
E/Z isomerism
optical isomerism
Stereoisomerism only occurs in compounds with..
.. a C to C double bond
2 diff groups attached to each C of the double bond
Why does sterioisomerism require the presence of a C to C double bond
the pie bond in the double bond restricts rotation so the E and Z isomers are different compounds. To switch between them bonds must be broken and reformed (chem reaction req)
Applying Cahn-Ingold-Prelog priority rule how is priority assigned
Atoms attached to the C=C (on the came side, left or right) are gived priority based on their atomic NUMBER.
Higher numb= increased priority.
Z-isomer?
When groups of higher priority are both on the same side of the double bond
E- isomer?
When groups of higher priority are diagonally placed across the C=C
Are the properties of the Z and E isomer the same?
No as they are different compounds
In longer groups, which atom’s atomic number is used for priority rules
If the first 2 atoms attached to a C in C=C are the same then the first point of difference should be used for priority rules
Criteria of cis/trans isomers
Req C=C bond
Req 2 different groups bound to Cs of C=C
AND
Req 1 of the groups bound to each C to be the same
Cis isomer?
Both groups which are the same are on the same side of the double bond (top or bottom)
Trans isomer?
The 22 groups which are the same are bound diagonally across the double bond
Addition reactions of alkenes? 4
Hydrogen in presence of nickel catalysts
Halogens
Hydrogen halides
Steam in presence of acid catalyst
What makes alkenes more reactive than alkanes
Pi bond: E- in pi bond are more exposed than in sigma bc they are on the outside of the double bond rather than directly between bonding atoms
name for alkene + hydrogen
Hydrogenation
Conditions req for hydrogenation of alkenes 2
Presence of nickel catalyst
(one H2 molecule per C=C bond)
name for halogen + alkene
Halogenation
At what temp can halogenation of alkenes occur and products
Room temp to give dihaloalkanes
Test for presence of alkene (C=C bond)
Add bromine water drop wise
Orange ti colourless, bromine is decolourised
