last minute memz Flashcards
Camph: Why water not be suitable solvent for this reaction?
- Boroneal and camphore are not soluble in water
- water would quench the NaBH4
Camph: why was it not necessary to use a reflux condenser for this reaction?
the reaction was over so fast that not much of the methanol would have evaporated
Ester: why were the acid base extractions you performed not successful in separating your reactant alcohol and product ester?
Both alch and ester are large non acidic organic compounds, so neither will ionoize or move into the water layer
Ester: would IR spec of the pure ester be useful in determining your known alcohol was pentanol or butanol?
No. Butyl and pentyl acetate would have the same functional groups so their IR spectra would essentially be the same.
Ester: Table: why is webmo so accurate for CH peaks but so inaccurate for the OH peaks?
In the real world, OH groups can H-bond, which has a large effect on chemical shift. In webmo, only 1 molecule is calculated so H-bonding can’t be taken into effect and the result is not accurate.
CH peaks can e calculated accurately without needing intermolecular forces
Camph: Why was isoborneal the major product?
The reaction is equilibirum, and the easiest and fastest attck is for the hydride to attack the bottom of the ketone
WEBMO: Briefly explain why using the cleanup button would lead to flawed results if used in between a
geometry optimization and NMR calculation.
The cleanup button is a lower level than the actual calculation. Using it would undo the work to get an
accurate geometry which will skew future calculations
Ester: why is the equilbirum constant for this reaction close to 1?
Carboxylic acids, and esters have similar stabilities so both sides of the reaction are similarly favorable
Camph: why is water used to purify camphor after the reaction is over?
Water is added to precipitate the organic compounds because as large netural organic compounds they are not solublle in water.
Camph: why does camphore has a shorter retention time in GC than in borneol or iso?
Camph has a shorter retention time because it cant show h bonding while iso/bor can. this means that camph has a lower boiling point and a shorter retention time
Webmo: In order to directly compare the WebMO heat of formation for 2 compounds, they must have
the same chemical formula and be calculated at the same level of theory. Why
Heat of formation is based on the energy consumed or released from individual atoms / particles. If 2
compounds have different formulas, they will be built from different numbers of parts, which will give
different energies regardless of which compound is more stable. Similarly, different levels of theory
will calculate different absolute energies regardless of stability.
Camph:Below are heats of formation for borneol and isoborneol Explain (1 sentence) how this data
shows which isomer is more stable? Also explain (1 sentence) why this is consistent with what you
learned way back in Chem 237?
Borneol: -464.3123 Hartrees
Isoborneol: -464.3143 Hartrees
Isoborneol is more stable because the energy is more negative. This is consistent because the OH
group is equatorial rather than axial.
Camph: It turns out that your answer to part E is irrelevant for explaining why isoborneol is the major
product. Why (1-3 sentences) is the relative stability of isoborneol and borneol not relevant to which
is the major reduction product?
The selectivity is controlled by which side of the C=O bond is easier for hydride to attack based on
sterics. This has nothing to do with which product is ultimately more stable.
(Alternate answer – the reaction is under kinetic control, not thermodynamic control. Product
stability is thermodynamics, while transition state stability is kinetics).
Webmo:In WebMO, why (1-2 sentences) is it necessary to do a geometry optimization before running
an NMR or partial charge calculation?
If the geometry isn’t optimized, then other physical properties won’t be calculated accurately since
atoms/electrons/bonds won’t be in the correct position
