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Post by bbiebelberg » Fri May 22, 2020 2:29 pm

Hello! I have two questions from NS FL3 C/P section.

Question 18
I chose A because I learned to consider resonance when determining hybridization states, and if resonance is possible, to use the lowest hybridization state. I saw that the lone pair on the imine nitrogen could resonate up into a double bond, pushing the C=C double bond electrons onto the left carbon to form a carbanion. In this case the nitrogen would have two double bonds and a positive charge, giving it sp hybridization. Is this not the approach we should follow for the MCAT?

Question 59
RN II is very clear to me, but RN IV is not. Why will drag from the viscous medium necessarily cause the cell to decelerate to 0 m/s, as opposed to possibly slowing it down to some other, lower speed?

One more random question that isn't specific to C/P -- when looking at several cyclic carbohydrates linked together, how do you determine the type of linkage? (1->4, 1->6, etc.). My question, really, is how do you count the carbons on a cyclic carbohydrate -- how do you determine which part of the ring is numbered 1?

Thank you.
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Re: NS FL3 C/P

Post by NS_Tutor_Yuqi » Sun May 31, 2020 1:46 am

18. I see what you're saying here. However, the resonance structure shown in the passage will contribute more to the overall structure since it is the lowest energy structure (the carboanion is unfavorable). Additionally, the wording of the question may be eluding to the fact that they want you to determine the hybridization of the structure that's drawn out through the phrase "as depicted in the passage".

59. Drag is a force that opposes the movement of the object. Since this is the only force acting on Cell 2 after it collides with Cell 1, it will eventually approach a velocity of 0. Another way to think about this is that the drag from the viscous liquid wouldn't suddenly disappear after the cell slows down to a lower speed.

The convention for naming monosaccharides is to start at the terminal carbon that is closest to the carbonyl carbon (which is either an aldehyde or ketone). In the cyclic structures, that would be the the carbon that is bonded to two oxygens. Therefore, in the disaccharide I've attached, you'll actually begin numbering at the carbonyl carbon on the left sugar, but start at the top terminal carbon that's closest to the carbonyl carbon on the right sugar.

I hope this helps! Let me know if I can elaborate further.
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