Orgo Ch 3 notes pt 2
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Are rings flat?
yes, but not really
What is the only flat ring that is saturated?
the three membered ring
A flat ring system has __. Why?
angle strain due to desire to be 109.5 degrees
In cyclopropane, all __ lie outside an imaginary triangle.
electron densities of sigma bonds
How strong are the sigma bonds attached? (cyclopropane)
barely hanging on
In cyclopropane, sigma overlap is __
usually very weak to exist (weaker than normal)
Cyclopropane has __ and __.
- angle strain
- torsional strain
What is the only way for cyclopropane to exist?
in eclipsed conformation because there are two carbons attached to one carbon
Why does it have to planar?
three points form a plane
Heat given off in reactions is somewhat indicative of __.
Rank the cycloalkanes by their relative ring strain.
- 3 and 4 membered rings: highest
- 5: not so much
- 6: most stable (perfect ring system; lowest in energy)
- to alleviate tension, it __
- if __, it would be __.
- not a square or planar, more like a butterfly
- perfectly eclipsed, it would be perfectly square or planar
- __ most comon ring size in nature (__)
- what is the most common?
- 2nd most common
Cyclohexanes go through __ and __.
- chair conformations
- ring flipping
Explain axial and equatorial.
- axial: parallel to imaginary axis that goes traight at or away from me
- equatorial: parallel to the molecule itself; to some equator
If the chair conformation has wedges, then what?
the wedges are coming at you
Even though you flip the chair, what?
your molecules stay up or down. The axial will become equatorial and vise versa. Cis remains cis. Trans remains trans
True or False:
cis and trans are the same as axial and equatorial.
- have nothing to do with them
True or False:
Explain reactivity in terms of cyclobutane.
not terribly rective in the form of a saturated molecule
Explain reactivity in cyclopentane.
- not the best because it isn't flat
- if flat all the H eclipse the other around the ring
parallel and alternate up and down
come in three sets of two parallel lines; each set is also parallel to two ring bonds; alternate between sides around the ring
Explain rules of flipping chair comformations.
- all axial become equatorial
- all equatorial become axial
- all up bonds stay up
- all down bonds stay down
__ are flagged by parallel H's __
- gauche interactions
- 1,3 diaxial interactions
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