The mechanisms of addition reactions Flashcards
why do we use curly arrows?
to show the movement of a pair of electrons in addition reactions
what do we mean by the term electrophile?
a species which is attracted to a region of high electron density
using your knowledge on electrophiles, what do you think an electrophilic addition reaction consists of?
an addition reaction, where two molecules react to form one molecule, and where the attacking molecule is an electrophile
what is heterolytic fission?
the breaking of a covalent bond so that both bonding electrons are taken by one atom
how are carbocations formed?
carbocations form when the double C=C bond is broken in the addition of hydrogen from a hydrogen halide, leaving one of the carbon atoms with a positive charge as its previously shared electron is used in the bonding of the hydrogen atom.
what are carbocations?
a positive ion in which the charge is shown on a carbon atom
which of the atoms in HBr are more electronegative?
the bromine atom
how can we tell which atom in a hydrogen halide is more electronegative?
fluorine is the most electronegative element in the periodic table, and the trend of electronegativity decreases the further away on the table you go from fluorine
what is an electron releasing group?
a group which pushes electrons towards the atom it is joined to
what is an unsymmetrical molecule? what are the conditions needed for one to form?
if both the alkene and the attacking molecule are unsymmetrical, then there are two possible products that could form as the atoms in the attacking molecule can be added in two different places
what makes an unsymmetrical alkene?
when the atoms on either side of the C=C bond are not the same. (eg. propene is unsymmetrical as one C on the C=C bond has two H while the other has one H and one C
what two products could be formed from the reaction between propene and hydrogen bromide? (both being unsymmetrical molecules)
2-bromopropane and 1-bromopropane
how do we know which of the products, either 2-bromopropane or 1-bromopropane is most likely to form?
2-bromopropane forms when a secondary carbocation is formed while 1-bromopropane forms when a primary carbocation is formed. as secondary carbocations are more stable than primary carbocations, they are more likely to form, the reason being the number of alkyl groups bonded to the carbocation
why are secondary carbocations more likely to form than primary carbocations?
carbocations with more alkyl groups joined to them are more stable because the positive charge of the carbocation is spread out by the electron releasing alkyl groups, so more alkyl groups means the charge is spread more.
what property do alkyl groups have?
they are electron releasing
