Functional Group Chemistry Flashcards
what does ADME stand for?
absorption, distribution, metabolism, excretion
name 4 features of a nucleophile
- nucleus-loving
- electron rich
- negative charge/lone pair of electrons
- double bonds
name 3 features of an electrophile
- electron-loving
- electron poor
- positive charge
what are leaving groups?
terminology used for ions or neutral molecules that are displaced from a reactant as part of a mechanistic sequence
how are leaving groups formed?
a consequence of a nucleophile attacking an electrophile, where the electrophile carries a suitable leaving group
what makes a good leaving group?
those that form stable ions or neutral molecules after they leave the substrate
what is heterolysis?
bond breaks such that both of the electrons stay with one of the atoms
what is homolysis?
bond breaks so that each of the atoms retains one of the bonding electrons
what is standard free energy?
the different energy levels between the reactants and the products
what is activation energy?
the energy difference between the starting material and the transition state
what happens to the boiling point of alkanes as molecular weight increases?
it increases
what are the ONLY intermolecular forces present in alkanes?
weak London forces
are alkanes reactive or unreactive?
unreactive
what do alkanes produce during combustion?
CO2, H2O and heat
during halogenation, what do alkanes react with?
chlorine and bromine
when can halogenation occur?
- at high temperatures
- in the presence of high energy light
what mechanism is halogenation?
radical mechanism
what are the three steps in a radical mechanism?
- initiation
- propagation
- termination
what happens during initiation?
- formation of radical
- light induced formation of chlorine radicals through homolysis from neutral chlorine
what happens during propagation?
- one radical is used to generate another radical
- the chlorine radical can now abstract a hydrogen from another neutral molecule CH4 producing a methyl radical
what happens during termination?
-the combination of two radicals to produce a neutral species
what is hyperconjugation, how does it occur and what does it result in?
it is a stabilising interaction that occurs when the electrons in a o bond interact with an adjacent unfilled p orbital or pi orbital. it results in an extended molecular orbital that increases the stability of the system
what two radicals are more stable than expected and why?
benzyl and allyl due to resonance:
- delocalisation of electrons
- partial radicals residing over several atoms instead of just one
what is resonance used to describe?
electron charge and delocalisation
why are cis isomers less stable than trans isomers?
there is a strain between the two larger substituents on the same side of the double bond
are alkenes more or less reactive than alkanes?
much more reactive
how are alkanes prepared? (3)
- cracking
- dehydrohalogenation
- dehydration
what type of reactions do alkenes undergo?
electrophilic addition
why do alkenes undergo electrophilic addition? (3)
- electrons in pi bond are accessible reactants
- they are nucleophilic and react with electrophiles
- electrons move from bond to electrophile
what are the two types of addition reactions in an alkene and what do they involve?
- homolytic (involves radicals)
- heterolytic (involves cations)
what is the rate limiting step in the addition of HX to an alkene?
carbocation formation
why is the stability of the carbocation important?
it controls the overall outcome of the reaction
what is Markovnikov’s rule?
in an electrophilic addition to an alkene, the electrophile adds in such a way as to form the most stable intermediate
what occurs in order to keep markovnikov’s rule?
-reaction proceeds via the most stable carbocation
-the electrophile adds to the sp2 carbon in the double bond that is the most substituted
-
what molecules add to alkenes to form markovnikov products in the absence of light or peroxide?
HCl, HBr, HI
what happens in a regioselective reaction?
one constitutional isomer is the major, or the only, product
what is determined by the stability of the intermediate carbocation?
the outcome of the product
are alkyl groups electron donating or withdrawing?
electron donating (weakly)
what is hyperconjugation
stabilising interaction between a p orbital and C-H o bonds on neighbouring carbons
do alkyl groups increase or decrease the concentration of positive charge on C+
decrease
in alcohols, what happens to the acidity as alkyl substitution increases? and what is this known as?
it decreases, known as a positive inductive effect
in alcohols, what happens to the acidity when the number of halogen substituents increases? and what is it known as?
it also increases, known as a negative inductive effect
how is ethanol produced?
industrially produced by fermentation of starch and grains
what is the toxic dose of methanol?
100mL
what is the toxic dose of ethanol?
200mL
how are more complex alcohols prepared? (3 main methods)
- hydration of alkenes
- hydrolysis of alkyl halides (nucleophilic sub reactions)
- reduction of carbonyl compounds
what 2 substances can reduce aldehydes and ketones? how do they work?
- sodium borohydride NaBH4
- lithium aluminium hydride LiAlH4
- they act as sources of hydride and as additions of H-H across C=O
what is the only substance esters can be reduced by?
LiAlH4
what is alkoxideformation?
reaction of alcohol with sodium metal
are high oxidation state metal salts good oxidising agents? why?
yes, as they are soluble in water
how does biological oxidation of alcohols occur in the body?
carried out by enzymes using NAD+ as a coenzyme
what is the function of alcohol dehydrogenase?
converts alcohol to aldehyde
what is the function of aldehyde dehydrogenase?
converts aldehyde to acid
what can the process of biological oxidation be inhibited by?
disulfiram
how can haloalkanes be used as anaesthetics?
accumulate in lipid membrane of nerve cells and interfere with transmission of nerve impulses
does an alkane or haloalkane have higher BP?
haloalkane
why do haloalkanes have higher BP than alkanes?
the greater polarisability of C-X bond
how can haloalkanes be prepared? (4)
- free radical substitution of alkanes
- electrophilic addition (H-X) to alkenes
- halogenation of alkenes or alkynes
- halogenation of alcohols
what happens to the rate of reaction with a given nucleophile when the size of the haloalkane increases?
decreases
what is the name of a one step Sn2 reaction mechanism?
concerted
what is nucleophilicity?
a measure of how readily a compound is able to react with an electron-deficient atom
what is polarisability?
a measure of how well a nucleophile can encroach on the orbital used for bonding in the electrophile
what is basicity? and how is it measured?
a measure of how well a compound is willing to donate a lone pair of electrons to a proton. it is measured using the acid dissociation constant Ka
