Introduction to Organic Chemistry Flashcards
Homolytic fission
refers to when a bond is broken, leaving two atoms with the same number of e-
free radical
a highly reactive species with an unpaired e-
explain why free radical substitution will never produce only one product
the bromine free radical is regenerated in the propogation step and can react with another ethane molecule or bromoethane to produce dibromoethane, which can then react with another bromine free radical. the cycle perpetuates until all of the hydrogens have been substituted
how can the formation of multiple substitution by products be minimized
increase concentration of ethane, because the chance the bromine free radical collides to form a mono substituted product, bromobutane, rather than colliding with another bromobutane to form a disubstituted product
heterolytic fission
when a covalent bond is broken and both electrons go to the same atom (one of the atoms)
electrophile
accepts a pair of electrons to form a dative covalent bond
why are alkenes more reactive than alkanes
- alkenes have a c=c bond, which is of higher electron density and thus is more attractive to electrophiles
- the pi component of a double bond is weaker than the sigma bond component, and can break more easily
what do alkanes vs. alkenes require to react
UV; alkenes can react under standard conditions because they are more reactive
what are the conditions required for an alkene to react with water
H3PO4 or H2SO4 catalyst at 300 deg. C
what are the conditions required for an alkene to react with hydrogen
nickel catalyst at 150 deg. C
what is the purpose of hydrogenation
Hydrogenation of unsaturated fats replaces the double bonds with a single bond through the addition of hydrogens, which bond to carbons. Double bonds in unsaturated fats prevent the fats from packing as tightly together, so hydrogenating it makes it saturated and can last longer on shelves. e.g. margarine
what does Markovnikov’s rule state
for asymmetrical alkenes, X (delta +) in the electrophile
Xδ+ – Yδ- will add to the carbon that has the most H atoms bonded to it (this will be the major product)
why is a tertiary carbocation the most stable
it contains the most alkyl groups, which are electron donating, thus, they donate electrons towards the C+, which stabilizes the positive charge
describe the movement of electrons in an electrophilic attack between electrons of the double bond and the bromine molecule
the pi component of the C=C double bond breaks heterolytically and one of the C atoms donates the pair of electrons to the delta positive Br atom. Meanwhile, the Br-Br bond breaks heterolytically and both electrons are taken by the negative Br which becomes a bromide ion (with full negative charge)
why does an alkene react much more readily with a hydrogen halide than with a halogen
in a hydrogen halide, a permanent dipole already exists (as the bond is polar due to the difference in electronegativity between the atoms). This means it is already attracted to the C=C. Whereas in a halogen, the dipole has to be first induced by the C=C.
