orgo lab quiz Flashcards
why can’t alkanes be used as starting materials to make compounds?
alkanes are unreactive because:
-they are very stable
-very consistent electron density
-they don’t have a functional group
-they are sp3 hybridized
functional groups are the center of…
reactivity
what mechanism can alkanes react with?
free radical mechanism
what are the steps of the free radical mechanism?
- initiation
- propagation
- termination
what happens during the initiation step?
you have a halogen and you need energy that overcomes the bond association energy inside the bromine molecule
the energy you’re applying has to be greater than or equal to the energy of the bond, so it will break in the middle. this is called hemolytic
homolytic bond cleavage
(you are generating the radicals, concentration of the radical goes up)
describe what happens during the propagation step
you are maintaining the concentration of the radical (you start with one Br radical and you end up with one Br radical)
termination
the radicals combine with each other
concentration of radicals goes down
how many steps are there in the free radical mechanism?
six steps (draw out all six for the quiz)
what applies to the stability of the radical?
-resonance
-hyperconjugation
what type of hydrogens are in cyclohexane?
secondary aliphatic (1 kind of hydrogen)
what is a mono-halogenated product?
we only want to halogenate one hydrogen
what is a limiting reagent?
the reactant that gets consumed first in a chemical reaction and therefore limits how much product can be formed.
the trend under light condition and dark condition is the…
same
why does the reaction under light condition take faster?
because you are applying energy to break the bond in the molecular bromine homolytically
what is the limiting reagent?
bromine
why don’t we watch the glassware with acetone?
we use dichloromethane instead of acetone because acetone reacts with bromine and will form bromoacetone and it will make you cry
what was the most reactive for this experiment?
isopropyl benzene
what was the least reactive for this experiment?
tert-butyl benzene
how do we determine the order sequence/reactivity?
We determined the order sequence because in the propagation step when the Br radical tries to extract a hydrogen from the hydrocarbon, it’s going to extract the most reactive hydrogen. The most reactive hydrogen is the one that’s going to form the most stable radical.
Explain why is a 1° benzylic radical more stable than a 1° aliphatic radical
Benzylic radicals are more stable than aliphatic radicals because of resonance effects
should the reaction occur under dark conditions?
no it shouldn’t happen at all but in reality it will because we are going to keep a little bit of light in the lab because we want to monitor the reaction
how do we monitor the progress of the reaction?
by the disappear of the brown color in bromine. when the brown color goes away the reaction in complete
On the basis order of stability of the radicals deduce the order of reactivity toward the radical bromination of the seven different types of hydrogens: (1) 1o aliphatic, (2) 2o aliphatic, (3) 3o aliphatic, (4) 1o benzylic, (5) 2o benzylic, (6) 3o benzylic, and (7) aromatic.
Most to least reactive:
3° benzylic, 2° benzylic, 1° benzylic, 3° aliphatic, 2° aliphatic, 1° aliphatic, aromatic
when you have two acids reacting with each other what happens?
the stronger acid acts as an acid the weaker acid acts like a base