CL 13- alkenes Flashcards
1
Q
unsaturated
definition
A
containing one or more multiple C=C bonds
2
Q
describe a C=C bond
types of bonds etc.
A
- consists of an overlap of electrons in the 2s subshell to form a sigma bond (3 electrons used)
- remaning electron contained within a p-orbital, which sideways overlap end-to-end to form a pi bond
3
Q
rotation of C=C bonds
A
no free rotation of the groups about the C atom, as the pi bond extends above and below the plane of the C atoms
4
Q
shape around C atom in alkene
A
- trigonal planar
- 3 regions containing electrons around each of the C atoms, which repel each other
- bond angle is 120°
5
Q
E/Z isomerism
explain concept
A
occurs in compounds with a C=C bond, where different groups are attached to each C atom of the double bond
6
Q
cis-trans isomerism
explain
A
- same conditions of E/Z isomerism, but one of the attached groups on each C atom of the double bond must be the same
- usually the cis isomer is the Z isomer, and the trans isomer is the E isomer
7
Q
how to identify E and Z isomers
Cahn-Ingold-Prelog (CIP)
A
- assign priority to atoms attached to each C in C=C
- the higher the atomic number, the higher the priority
- if the priority groups are on the same side of the double bond, it is a Z isomer
- if the priority groups are diagonal, it is an E isomer
7
Q
why are alkenes reactive?
A
- pi bond weaker than sigma bond and easily broken
- unsaturated, so molecules can add across the double bond
- double bond has high electron density, so attractive to electrophiles
7
Q
testing for alkenes
test, result, equation
A
- bromine water
- from orange turns colourless
- C₂H₄ + Br₂ –> C₂H₄Br₂
7
Q
electrophile
definition
A
electron pair acceptor
8
Q
ethene + hydrochloric acid
mechanism for electrophilic addition for alkenes
draw and check with written answer
A
- dipoles on H-Cl (H + and Cl-)
- curly arrow from middle of double bond to H
- curly arrow from middle of H-Cl to Cl
- H connected to C
- C with positive charge, Cl with minus charge, curly arrow from lone pair of Cl to C+
- product of chloroethane
8
Q
A
8
Q
A
