1. Introduction to Org chem Flashcards
define homolytic fission
breaking of covalent bond such that one electron goes to each of the atoms, forming free radicals
define heterolytic fission
breaking of covalent bond such that both electrons go to the SAME atom, forming +ve and -ve ions (cation being the carbocation)
what kind of bond cleavage forms free radicals?
homolytic fission
electrophiles are lewis acids or base?
acid
characteristics of electrophiles [3]
- are electron deficient
- attracted to regions of -ve charge or electron rich regions
- may possess an empty orbital to accept election pair
characteristics of radicals
contains unpaired electron formed from the homolytic fission of a covalent bond
does steric hindrance increase or decrease a moelcule’s reactivity? why?
decrease. prevents approach of an attacking reactant and either prevents reaction from taking place or lowers reactivity of a particular site within molecule
what is the electronic effect?
can be either electron withdrawing or donating.
An atom or a group of atoms can increase/decrease electron density to a compound. can understand it as the momentary giving/receiving of electrons
state the 2 broad groups of isomerism. differentiate the 2.
constitutional isomerism and stereoisomerism
constitutional: same molecular formula but diff structural formula
stereoisomerism: same molecular formula, same structural formula but diff spatial arrangement of functional groups
prefix name for -NO2
nitro-
prefix name for R-C=O [carbonyls]
oxo-
prefix name for -NH2
amino-
prefix name for -OH
hydroxy-
prefix name for -CN
cyano-
electrophilic addition occurs only in ___?
aka electrophiles added
alkenes
addition reactions occurs when compound is saturated or unsaturated?
unsaturated aka double bonds aka C=C or C=O bonds
nucleophilic addition occurs in what kinds of compounds? [2]
ketones and aldehydes
define hydrolysis
a reaction which water is used to break a bond
define condensation reaction
2 molecules react tgt to form a bigger molecule with elimination of small molecules eg. H2O, HCl
oxidation occurs when ___ [4]
hint: what kinds of atoms are added/removed
- oxygen from oxidising agent is added
- H atom removed
- loss of electron
- increase in O.N
state the 3 kinds of constitutional isomerism
- chain isomerism
- positional isomerism
- functional group isomerism
what kind of constitutional isomerism do these compounds show?
chain isomerism
- essentially the same molecular formula C4H10 but differs in straight chain vs branched chain
what kind of constitutional isomerism do these compounds show?
positional isomers
- functional groups located at different part of the same carbon skeleton
what kind of constitutional isomerism do these compounds show?
positional isomers
- functional groups located at different part of the same carbon skeleton
what is functional group isomerism? [2]
criteria to fulfill
1. both compounds have SAME molecular formula
2. but have different functional groups
cis isomer has 2 identical groups on same/opposite side of the double bond?
same side
cis-same
for cis-trans isomers, cis isomers has higher/lower boiling point than their respective trans-isomer? explain
higher. cis isomers have higher polarity so additional pd-pd forces require more heat energy to overcome
criteria for enantiomerism [3]
- forms non-superimposable mirror image
- contains chiral centres
- does not have internal plane of symmetry
a chiral carbon is ___-hybridised
type of hybridisation: sp/sp2/sp3 ?
sp3
define racemic mixture
when theres is equal proportions of (+) and (-) enantiomers formed
characteristics of meso compound [3]
- superimposable mirror image even though they contain chiral centres
- contains internal plane of symmetry [which causes point 1]
- optically inactive
name the type of hybridisations & describe [3]
- sp hybridisation
- 1 2s orbital combine with 1 2p orbital to form 2 identical sp orbitals
- occurs when 2 σ bonds & 2 π bonds are formed - sp2 hybridisation
- 1 2s orbital combine with 2 2p orbital to form 3 identical sp2 orbitals
- occurs when 3 σ bonds & 1 π bond is formed - sp3 hybridisation
- 1 2s orbital combine with 3 2p orbital to form 4 identical sp3 orbitals
- occurs when 4 σ bonds are formed
for IUPAC Naming, suffix is always the principal functional group. when there are more than 1 functional group, what is the order for precedence?
carboxylic acid / acyl halide / aldehyde / ketone > alcohol > amine > alkene
characteristics of nucleophiles [3]
- are electron rich
- attracted to regions of +ve charge or electron deficient regions
- usually molecules with at least 1 lone pair of electrons
criteria for cis-trans isomers [2]
- restricted rotation in certain parts of the molecule due to π bond
- 2 different groups attached to the same atom of the π bond
why is the smallest cycloalkene to show cis-trans isomerism is cyclooctene?
the min no. of carbons in cycloalkanes to display cis-trans isomerism is 8. a cycloalkene with less than 8C gives only a cis isomer as the existence of a trans isomer will give rise to severe ring strain & hence instability.
what’s the no. of possible cis-trans isomers present in a compound?
2^m , where m is the no. of double bonds that gives rise to cis-trans isomerism
what’s the no. of enantiomers present in a compound?
2^n, where n is the no. of chiral centres
what’s the no. of stereoisomers present in a compound which exhibits both cis-trans isomerism & enantiomers?
2^m+n, where m is the no. of double bonds exhibiting cis-trans isomerism & n is the no. of chiral centres exhibiting enantiomerism
name all mechanisms for each functional group
- alkanes - free radical sub
- alkenes - electrophilic addition
- arenes - electrophilic substitution
- halogenoalkanes - nucleophilic sub
- carbonyls - nucleophilic addition
