Chemistry 14C Discussion Board

#21

Justin — Fri, 20 Nov 2009 22:11:09 GMT

How does the ammonium group work in affecting the pKa values?

How far does the effect of the NH3 extend to? (At what point should we ignore the NH3.)

Forum: Practice Problems

spring 2008 midterm 2 question 5

Danielle — Fri, 20 Nov 2009 21:20:36 GMT

I know the midterm has passed, but I have a question about one midterm still.

Question 5 asks for the H-NMR integral for A,B, and R. I was wondering, why is it 4 for A and B? I would have thought 2, unless A is the same as S, and B and U are the same. But why would that be?

thank you!

Forum: Old Exam and Miscellaneous Questions

Hydrogen Bond Acceptors

davidpollack — Fri, 20 Nov 2009 21:14:08 GMT

I'm a little unclear on why fluorine can not be a Hydrogen Bond Acceptor. In lecture on Monday, Dr. H talked about what qualified as hydrogen bond acceptor and said it could be 1. a neutral, highly electronegative atom with lone pairs or 2. an anion. Under the first category, he said only oxygen and nitrogen could work as acceptors. My question is, why not fluorine? It is also small and neutral, very electronegative, and has lone pairs. Can anyone explain why it doesn't accept hydrogen bonds?

Forum: Old Exam and Miscellaneous Questions

#14

Justin — Fri, 20 Nov 2009 21:07:10 GMT

For #14, are we supposed to memorize or simply look up the pKa of the hydronium ion? Or is there a way to figure it out based on other common pKa's?

Forum: Practice Problems

Question 19

Justin — Fri, 20 Nov 2009 19:40:27 GMT

Wouldn't the polar bear prefer the oil layer? The vinegar layer is polar, and hence would dissolve the bear.

(Like dissolves like.)

(This post is only semi-serious.)

Forum: Practice Problems

Electrostatic interactions

kturner5 — Thur, 19 Nov 2009 22:34:42 GMT

Do ALL Noncovalent Forces have electrostatic attraction?

Forum: Concept Focus Questions

Boiling Point

kturner5 — Thur, 19 Nov 2009 22:32:16 GMT

Why does boiling point increase when attraction (strength of IMforces) increases?

Forum: Concept Focus Questions

#4

kdyang — Tue, 17 Nov 2009 03:45:48 GMT

Does spacial arrangement of the methyl groups in molecules E and F affect their H-NMR spectrum at all? Do they have the same spectrum?

Forum: Midterm Exam 2

Fall 2008 #6

amitp — Mon, 16 Nov 2009 23:28:43 GMT

The answer to this question shows 2 carbonyl peaks in zone 4, one for the conjugated ester and one for the nonconjugated ester. I understand why the chemical shifts for the these two groups are different, and consequently there are 2 peaks. But if the conjugated peak was not conjugated, would there still be 2 peaks? In other words, if there are nonconjugated 2 esters in a molecule, are there 2 carbonly peaks in zone 4? Also, if there are 2 different carbonyls (say an aldehyde and a carboxylic acid), would there be 1 or 2 peaks in zone 4?

Forum: Old Exam and Miscellaneous Questions

Magnetic Induction

kdyang — Mon, 16 Nov 2009 22:55:47 GMT

What is magnetic induction, and why does it occur in benzene rings? When else does it occur?

Forum: Old Exam and Miscellaneous Questions

Winter 2009 #10a

kylenguyen90 — Mon, 16 Nov 2009 12:04:21 GMT

I don't know how we can be sure that nitrogen atoms are present in a molecule based solely on knowing that the m/z (M) value is odd. We can't make this conclusion because the nitrogen rule only tell us whether the number of nitrogen atoms is even or odd (if there are nitrogen atoms in a formula). Is this right? Kyle Nguyen

Forum: Old Exam and Miscellaneous Questions

winter 2009 midterm 2 #13c

am — Mon, 16 Nov 2009 10:49:41 GMT

Does the 5.51ppm chemical shift correspond to the CH2 in the resulting molecular structure? If so, I'm confused as to why that is because I thought proton NMR shifts for RCH2X (X=Cl,Br,I) was supposed to be around 3.5ppm.

Forum: Old Exam and Miscellaneous Questions

Spring 2008 #5

bchiang — Mon, 16 Nov 2009 09:14:20 GMT

Hi,

I have a question on #5 in the Spring 2008 midterm. How do you get 5.2 for the H-NMR chemical shift for "R"?

Forum: Old Exam and Miscellaneous Questions

Identifying Planarity?

jamar — Mon, 16 Nov 2009 09:00:19 GMT

Could someone explain how Crystallography helps determine of a molecule is planar (Spring 2009, Lecture 1, Exam 2, Question 11D). Does this tie into the "topographical map" analogy, where it shows how far various atoms stick out in a sense towards the viewer? Or is this only once the computer program has spaced all the atoms out?

Forum: X-ray Crystallography

Winter 08 #8

vnguyen — Mon, 16 Nov 2009 08:43:45 GMT

For part (c), I don't understand how they got four signals with integral=2 and 2 or integral >3. I see six signals with an integral of 2, and I don't see ANY with an integral of three or more. These integral problems have been giving me a lot of issues, so can someone please explain it to me?

Forum: Old Exam and Miscellaneous Questions