Lecture Quiz 3 - Lectures 10-15 Flashcards
(69 cards)
How many H atoms does each Carbon atom in a chair have?
2 H
How many axial and equatorial H atoms does a Carbon atom in a chair have?
1 axial H, 1 equatorial H
How many upper/lower face H atom does a Carbon atom in a chair have?
1 upper H, 1 lower H
1 up, 1 down
When rotating bonds to flip a chair, which groups switch and which groups stay the same?
a) axial and equatorial
b) up/down
Axial groups switch to eq
Eq groups switch to axial
up/down groups stay the same
What type of strain is present in a boat conformation? What is it caused by?
Transannular strain - caused by steric hindrance between H and H atoms
Which conformation has higher Energy? Chair or Boat?
Boat because of the eclipsing/torsional strain
Which group has higher Energy? Equatorial groups or axial groups?
Axial because parallel axials bump causing steric hindrance
Eq groups have a lot of space and minimal steric hindrance so they are lower in E
Since disubstituted cyclohexanes have a restricted rotations…?
we can get fixed orientations:
2 groups on the same side of the ring = cis
2 groups on opposite sides of the ring = trans
Why do we prefer smaller axial groups?
Smaller axial groups results in lower Energy
Ex: F vs H
List the order of least to greatest steric hindrance of:
1* C, 2C, and 3C
1C
2C
3*C – most steric hindrance because bonded to the most methyl groups
List the order of preference:
all axial groups vs all eq groups
if axial groups are present:
larger axial groups vs smaller ones
Prefer all equatorial groups
If we must have axial groups, fewer and smaller axial groups are prefered
List the 2 ways to break up a molecule/bond
1) homolytic cleavage
2) heterolytic cleavage
What does homolytic cleavage form?
When do they typically happen?
What is delta H equal to? Is this exo or endothermic?
Homolytic cleavage forms radicals/unpaired electrons.
Typically happen when we have non-polar solvents and molecules in the gas phase.
Delta H = bond Energy
Endothermic
How many electrons are moved in the process of homolytic cleave? What symbol is used to represent this movement of electrons?
1 e- movement / single prong
What does heterolytic cleavage form?
When do they typically happen?
What is delta H equal to? Is this exo or endothermic?
Heterolytic cleavage forms ions.
Typically when we have polar solvents and molecules in the liquid phase.
Delta H = Variable
endothermic
How many electrons are moved in the process of heterolytic cleave? What symbol is used to represent this movement of electrons?
2 e- movement / double prong
What are the characteristics of alkane reactions?
-hard to react with
-“parafin” - poor affinity, don’t react with much
-do react with strong oxidizing agents
What are some molecules that alkanes will react with?
O2 – strong oxidizer, leads to combustion which is hard to control
Halogens X2 – F2, Cl2, Br2 (Not I2)
What is Halogenation? Is it the same thing as a radical chain mechanism?
Halogenation = when alkanes and halogens react. It refers to what bonds are changing - what is added/changed. The name of whatever halogenation rxn you’re dealing with is describing what we’re doing.
They are exothermic and will form stronger bonds
No they are not
How does halogenation work?
Radical chain mechanism. it is the name of the mechanism, not the RXN. It’s how electrons flow and what steps occur
What are the 3 steps of a radical chain mechanism?
1) initiation step
2) propagation step(s)
3) termination step(s)
The Initiation step ______ radicals / ______ bonds
creates radicals / breaks bonds
The initiation step is (sometimes/always) (exo/endothermic). It is (rare/common).
Initiation step: ALWAYS ENDOthermic, RARE
Propagation steps _____ radicals / ______ bonds
Propagation steps exchange radicals, exchange bonds
