reactivity 3.4 Flashcards
define nucleophile
a reactant that forms a covalent bond to its reaction partner (electrophile) by donating both bonding electrons to form coordination bonds
examples of nucleophiles (name a few)
H2O, NH3, alcohols, amines, OH-, singular halogens (Cl)
define electrophile
a reactant that forms a covalent bond to its reaction partner (nucleophile) by accepting both bonding electrons to form coordination bonds
examples of electrophiles (name a few)
hydrogen halides, double halogens (Cl2), H2O, halogenoalkanes, H+, NO2+, CH3+
define coordination bond
covalent bonds where both electrons come from the same atom
why are nucleophiles usually attracted to electrophiles & vice versa?
nucleophiles are usually electron rich, and attracted to positive charges
electrophiles are usually electron deficient OR have an electron deficient region (polar), and attracted to negative charges
why are halogenoalkanes polar?
because the halogen atom is more electronegative than carbon, which exerts a stronger pull on the shared electrons in the C-Halogen bond
this creates partial positive and negative charges on halogen and carbon respectively
in this example, why does a substitution occur?
CH₃Cl + OH- → CH₃OH + Cl-
because OH- (a nucleophile) is attracted to the electron deficit in the carbon, where it then “attacks” the carbon and takes the spot of Cl, kicking it out and causing a substitution
why can halogenoalkanes be converted into many different classes of compounds?
because the halogen atom can be substituted by a variety of nucleophiles
for the nucleophile to donate an electron pair to the substitution molecule and form a new bond, another bond must break.
what will occur to allow this?
a leaving group will break away from the substrate molecule
why do halogens make good leaving groups? x2
because they form relatively weak bonds with C
high electronegativity of halogen also makes the C atom electron deficient, and thus susceptible to nucleophilic attack
watch a video on nucleophilic substitution with both halogenoalkanes and neutral species
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define heterolytic fission
when a covalent bond breaks, one of the products gain both of the shared electrons
this makes one product with a positive charge, and one with a negative charge
heterolytic fission is opposite to what process?
when a nucleophile donates a pair of electrons to an electrophile to form a coordination bond
what do these 3 arrow represent?
- → or ←
- ⤻ or ⤺
- ↼ or ⇀ (but curved)
- represents reaction pathway (reactants to products)
- transfer of 2 electrons (eg. in heterolytic fission)
- transfer of 1 electron (eg. in homolytic fission)
why are alkenes more reactive than alkanes?
because double bonds have a higher electron density which makes it more attractive to electrophiles
what are addition reactions?
a type of reaction occurring at the double bond, where one bond is broken and opens up two new bonding positions on the C atoms
saturated vs unsaturated compounds
saturated = has only single bonds
unsaturated = has at least 1 double bond
how does the electrophile get distributed in an addition reaction?
xy = electrophile
the x attaches to one carbon and the y attaches to another. note that it is not possible for both x and y to attach to the same carbon
hydration converts alkenes into what type of compound?
alcohol
what additional component is added to hydration reactions? why?
a strong acid catalyst (eg. H2SO4) (often concentrated (conc.)) because water is usually a poor electrophile in hydration reactions
why is this hydration reaction important?
CH2CH2 → CH3CH2OH
creates ethanol, which is a useful solvent
__ react with __ to produce dihalogeno compounds
halogens react with alkenes
2 unique characteristics of an addition reaction with halogens
occurs quickly at room temp (spontaneous)
observation of a loss of colour
bromine is often used to distinguish between alkanes and alkenes. how/why?
bromine water reacts with alkanes through a radical (has a single electron) mechanism, which requires UV light to initiate reaction
Br2 reacts readily with alkenes, and does not require UV light as the bromine is attracted enough to the extra electrons
_____ react with __ to produce halogenoalkanes
hydrogen halides react with alkenes
order of reactivity for addition reactions with hydrogen halides x3, why?
HI > HBr > HCl
iodine has the largest radius, which means longer bonds that are easier to break, allowing it to react more readily
define most reactive
will react with the least amount of energy/most readily
