Definitions Flashcards
Define an enantiomer
1 of 3 definitions
Either of a pair of chemical compounds whose molecular structures have a mirror-image relationship to each other
One of two stereoisomers that are mirror images of each other that are non-superposable
non-superimposable mirror-image structures
Define a nucleophile
A chemical species with an electron rich atom that is capable of donating a pair of electrons
Lewis basis (proton donator or electron pair donator)
Define an electrophile
A chemical species with an electron deficient atom that is capable of accepting a pair of electrons
Lewis acids (proton acceptor or electron pair acceptor)
Define a primary alcohol
An alcohol with 1 carbon directly attached to the C-OH functional group
Define a secondary alcohol
An alcohol with 2 carbons directly attached to the C-OH functional group
Define a tertiary alcohol
An alcohol with 3 carbons directly attached to the C-OH
Define ragiochemistry.
Regiochemistry refers to how certain reactions end up forming one constitutional isomer over another
Regioisomers result (different products)
Ragioselective - reaction has a preference for forming one regioisomer over another.
What is a pair of non-superimposable mirror-image structures called?
An enantiomer
What is a heteroatom?
Any atom other than C and H in organic chemistry
What are SN1 and SN2 reactions ?
Nucelophilic substitution reactions
1 = unimolecular (substrate only) 2 = biomolecular (substrate and nucleophile)
Write a note on how an SN1 reaction occurs.
2
The SN1 reaction proceeds stepwise.
The leaving group is removed which forms the carbocation
Carbocation is attacked by the nucleophile.
The deprotonation of the protonated nucleophile takes place to give the required product
Write a note on how SN2 reactions occur.
SN2 occurs in one step, one bond is broken and one bond is formed in the same step
The nucleophile approaches the carbon atom to which the leaving group is attached.
As the nucleophile forms a bond with this carbon atom, the bond between the carbon atom and the leaving group breaks.
What can prevent SN2 reactions?
steric hindrance.
The reaction will only proceed if the empty orbital is accessible.
The more groups that are present around the vicinity of the leaving group (alkyl halides), the slower the reaction will be.
That’s why the rate of reaction proceeds from primary (fastest) > secondary»_space; tertiary (slowest)
What can prevent SN1 reactions
Carbocation stability
Since the first step of the SN1 reaction is loss of a leaving group to give a carbocation, the rate of the reaction will be proportional to the stability of the carbocation.
Carbocation stability increases with increasing substitution of the carbon (tertiary > secondary»_space; primary) as well as with resonance.
Differences between SN1 and SN2
3 +3
SN1
- rate of reaction is unimolecular
- two step mechanism
- carbocation formed as intermediate
SN2
- rate of reaction is bimolecular
- 1 step mechanism
- carbocation not formed as intermediate
Define isomers
Each of two or more compounds with the same formula but a different arrangement of atoms in the molecule and different properties.
Define chain isomerism
Different arrangements of carbon atoms leading to linear and branched chains
Define structural/constitutional isomers.
Are compounds with the same molecular formula
but different structural formulas
Define positional isomerism.
In position isomerism, the basic C skeleton remains unchanged but important groups are
moved around on that skeleton
Define functional group isomerism.
isomers contain different functional groups,
that is, they belong to different families of compounds (different homologous series
Classify isomerism.
Structural/constitutional
Sterioisomers
What is sterioisomerism?
Isomers that comprise the same parts but differ in spatial orientation are termed as stereoisomers
What are the two types of sterioisomers?
Conformational
Configurational/geometric
What is conformational isomerism?
a form of stereoisomerism in which the isomers can be interconverted just by rotations about formally single bonds (refer to figure on single bond rotation)
What is configurational/geometric isomerism?
stereoisomers that cannot be converted into one another by rotating the molecule around a single bond
Cis-trans isomerism
List the different types of structural/constitutional isomerism.
Carbon chain isomerism
Functional group isomerism
Positional isomerism
What is an E alkene?
A trans alkene
2 of same atom on different sides of double bond
What is a Z alkene?
A cis alkene
2 of same atoms on same side of double bond
Define a dehydrohalogenation reaction.
An elimination reaction in which a H and a halogen are removed by a base to form a pi bond
Define an addition reaction.
A reaction in which 2 or more reactants combine to form products
Define tautomerization
The process of converting one tautomer into another
Catalysed by both acid and base
Define tautomers
Constitutional isomers that differ in the location of a double bond and a hydrogen atom
What is an enol form?
Double bond and Hydrogen run longitudinally parallel to each other
What is a keto form?
Double bond and hydrogen run latitudinally parallel to each other
Define a sigma bond
A sigma bond is formed by the head-on overlap of two orbitals
Define a pi bond
A pi bond is formed by the sideways overlap of p orbitals
What are the main differences between pi bonds and sigma bonds?
(5)
Sigma = head on overlap, pi = sideways overlap
Sigma = s or p orbitals Pi = only p orbitals
Sigma determines shape of molecule, pi does not
Sigma is a strong bond, pi is not
Free rotation about sigma, restricted rotation about pi
What is a chiral centre?
Chiral centre is an asymmetric tetrahedral carbon atom that is bonded with four different groups.
What is a leaving group?
2
A leaving group is an atom or group of atoms that are able to break away from a molecule with a lone pair, breaking the bond between it and the molecule
It acts as the opposite of a nucleophile; instead of donating electrons to form a covalent bond, it breaks that bond and takes the electrons as it leaves
