Final Exam Flashcards
(39 cards)
How can you remember which solvent to use with which reactant?
Remember that “like dissolves like”.
Polar solvents are best for dissolving polar reactants (such as ions); nonpolar solvents are best for dissolving nonpolar reactants (such as hydrocarbons).
What is a polar solvent?
Solvents with large dipole moments (atoms with very different electronegativities are bonded together).
–Ex. Oxygen bound to Hydrogen
What is a non-polar solvent?
- -Lacks partial charges
- -Bonds are between atoms of similar electronegativity
What is a protic solvent?
A solvent with O-H or N-H bonds, which allows hydrogen bonding to occur
- -Decreases the reactivity of nucleophiles
- -Reactivity of Nu- increases down a column
What is a aprotic solvent?
A solvent that lacks O-H or N-H bonds. These solvents cannot hydrogen bond
–Reactivity of Nu- increases up a column
What are some examples of polar aprotic solvents?
Acetone, DMF, DMSO,
What are some examples of polar protic solvents?
Ammonia, water, methanol, ethanol, acetic acid
Do vinylic halides undergo Sn2?
NO
Do phenols and aryl halides undergo Sn1, Sn2, or neither?
NEITHER
In reacting with an epoxide, which carbon will a nucleophile attack in acidic solution?
The epoxide oxygen will be protonated first and the nucleophile will attack the MORE substituted carbon
In reacting with an epoxide, which carbon will a nucleophile attack in basic solution?
The epoxide oxygen will be protonated first and the nucleophile will attack the LESS substituted carbon
What is necessary for a reaction to undergo elimination by the E2 mechanism?
- -A anti-parallel beta hydrogen (the base will go for the lease sterically hindered hydrogen which will produce the most stable double bond)
- -A strong bulky base
What does it mean when a system is conjugated?
A conjugated system has a region of overlapping p-orbitals, bridging the interjacent sigma bonds. They allow a delocalization of pi electrons across all the adjacent aligned p-orbitals. The pi electrons do not belong to a single bond or atom, but rather to a group of atoms.
When is Huckle’s Rule used and what is it?
[1] The molecule must be planar
[2] The molecule must be cyclic
[3] Every atom in the ring must be able to participate in delocalizing the electrons by having a p-orbital or an unshared pair of electrons.
[4] Follows the 4n+2 (where n=0,1,2,3,etc) rule for number of pi electrons
–Thus systems with 2,6,10,14,18, etc. pi electrons are considered aromatic
Which factor generally has the largest influence on stability, inductive or resonance effects?
Resonance (resonance trumps everything, except when the atom of interest is directly bonded to a large atom. Then surface area delocalizes electron density the most)
When is BH4 used?
To convert an aldehyde to a primary alcohol (preferentially attacks the carbonyl group over a double bond)
When is LiAlH4 used?
To convert a ketone into a secondary alcohol(preferentially attacks the carbonyl group over a double bond)
What is the result of a hydroboration-oxidation reacction with an alkene?
Anti-markovnikov addition of H and OH
–Syn addition ONLY
What is the result of a hydroboration-oxidation reacction with an alkyne?
Anti-markovnikov addition of H and OH (however remember that there is tautomerization from the enol to the keto)
–Syn addition ONLY
What type of addition happens in a halogenation reaction?
Anti-addition
What do epoxides ( –CO3H groups) do?
Convert alkenes to epoxides (remember mCPBA)
What reagents are needed to perform hydration on a terminal alkyne?
H2O, H2SO4, HgSO4
the enol is formed first and tautomerizes to the keto
What does tautomerization do?
It moves the C=C double bond to a C=O double bond (enol to keto)
–Tautomers are constitutional isomers that differ in the location of a double bond and a hydrogen atom. Two tautomers are in equilibrium with each other ( but the more stable keto is favored)
What reagents are needed to perform hydration on a internal alkyne?
H2O and H2SO4
the enol is formed first and tautomerizes to the keto
