CHEM10006 Study Guide - Final Guide: Trigonal Planar Molecular Geometry, Sigma Bond, Nucleophilic Substitution
12 Jun 2018
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Each asymmetric centre has two possible configurations; a
molecule with n asymmetric centres has a maximum of 2
n
stereoisomers e.g. 2 centres has 4 stereoisomers
Nucleophile: Electron rich species that can donate electrons;
all molecules or ions with a free pair of electrons or at least
one pi bond can act as nucleophiles - often bases where the
stronger the base the better the nucleophile (can remove
protons)
If given a nucleophile such as EtONa, (Et = ethyl), just pay
attention to the oxygen (O
_
) which can act as a nucleophile
(sodium is irrelevant)
Electrophile: Positively charged or neutral species that is
electron deficient so can accept electrons
Carbocation: A molecule having a carbon atom bearing three
bonds and a positive formal charge; generally unstable, and
are intermediates in alkene reactions
Carbocation stability: Increases with neighbouring carbon
atoms , neighbouring carbon-carbon double bonds, and
adjacent lone pairs; the more substituted the central carbon,
the more stable it is
Carbocation rearrangement: Rearrangements that occur
when an entire bonding pair of electrons in a carbocation
migrate to a carbocation from one of its neighbours;
favourable when a new, more stable carbocation is formed;
migrations of a bonding pair of a hydrogen is a hydride shift
and of an alkyl group is an alkyl shift
Inductive effect: An electronic effect due to the polarization of
sigma bonds within a molecule or ion, typically due to an
electronegativity difference between the atoms at either end
of the bond; the transmission of charge through a chain of
atoms results in a permanent dipole in a bond
Hyperconjugation: The stabilising interaction that results
from the interaction of the electrons in a pi-bond with an
single bonds
4. View the molecule so that you are looking down the
bond from carbon to group 4
5. Anticlockwise: S, clockwise: R
If the lowest priority substituent (normally hydrogen) is
pointing out of the page: reverse the
anticlockwise/clockwise rule
Addition polymers
Radical polymerization: Polymerization with a single electron,
free radical involved, needs a catalyst initiator
Regiochemistry: Any process that favors bond formation at a
particular atom over other possible atoms
Heterocyclic aromatics: Compound where one or more
carbon atoms of the ring are displaced by atoms of other
elements, eg. pyridine, pyrrole, adenine
Nomenclature
Intermediates: Boat, twist-boat, half-chair
Axial: Hydrogens face up or down
Equatorial: Hydrogens are lateral/horizontal with the equator
Equatorial substituents result in more stable conformation due
to decreased steric interactions
Steric strain: High strain leads to instability and high energy
bonds; caused by unfavourable bond angles and eclipsing
interactions
Alkenes
●Double bond, planar, trigonal planar, head to head
overlap of SP
2
orbitals gives rise to a sigma bond;
sideways overlap of the P orbitals gives rise to a pi
bond (Pi bond weaker than sigma due to less efficient
orbital overlap)
●Stereoisomers possible due to lack of rotation about
C=C bond
E/Z Nomenclature
1. Assign priorities to the groups at each end of the
double bond (high/low at left and same at right) in
same as as for R/S
2. If high priority groups are on the same side: Z,
opposite side: E
Undergo addition reactions: driving force: overall replacement
Document Summary
Single bonds bond from carbon to group . View the molecule so that you are looking down the. If the lowest priority substituent (normally hydrogen) is pointing out of the page: reverse the anticlockwise/clockwise rule. Radical polymerization: polymerization with a single electron, free radical involved, needs a catalyst initiator. Regiochemistry: any process that favors bond formation at a particular atom over other possible atoms. Heterocyclic aromatics: compound where one or more carbon atoms of the ring are displaced by atoms of other elements, eg. pyridine, pyrrole, adenine. Equatorial substituents result in more stable conformation due to decreased steric interactions. Steric strain: high strain leads to instability and high energy bonds; caused by unfavourable bond angles and eclipsing interactions. Stereoisomers possible due to lack of rotation about. Assign priorities to the groups at each end of the double bond (high/low at left and same at right) in same as as for r/s.
