Thursday, November 7, 2013

Chapter 6

Any questions on Chapter 6 material? Post them here.
Note: Dr Fraser Hof will be teaching material from Chapter 6 in the week starting November 18. I will still be running my office hours as normal that week.

50 comments:

Anonymous said...

will midterm #2 be just on chapters 4 and 5?

Scott McIndoe said...

Yes, but it will draw on what you learned in earlier chapters, too.

Anonymous said...

How do non-polar solvents dissolve non-polar solutes? Do London forces contribute to the dissolving through inducing momentary dipoles or are those interactions too short lived?

Scott McIndoe said...

Yes, through London dispersion forces.

Anonymous said...

Is lecture help in Elliot still available Monday to Wednesday?

Scott McIndoe said...

Not from me, sorry. The university is closed on Monday, I have no regular hours on Tuesday and I am at convocation on Wednesday. I suspect the drop-in will be closed, too, but I'm not absolutely sure.

RobinT said...

The drop in centre in Elliot is closed Nov 11 to Nov 15.

RobinT said...
This comment has been removed by the author.
Anonymous said...

Are double/triple bonds more polar than single bonds?

Why are double/triple bonds more reactive? I always thought the bonds were stronger, more stable, and thus less reactive

RobinT said...

1056: The bond strength and the stability are two different things. Yes, the bond strength of a double or triple bond is greater than a single bond. This bond strength (bond dissociation energy) is the measure of the energy of breaking that bond. The reactivity on the other hand does not require that bond to be broken. To be reactive it needs to share electrons with another atom. In a multiple bond there are more electrons being shared between two atoms than in a single bond, and that greater electron density in between the two bonding atoms makes the multiple bond more reactive.

Scott McIndoe said...

To follow up on what Robin said... multiple bonds do tend to be more polar, because the electronegative atom is able to pull more shared electrons towards itself. Acetonitrile, H3CCN, for example, is more polar than you'd expect because the N shares 6 electrons with the C and can draw all of them towards itself.

Anonymous said...

Will a portion of chapter 6 be covered on the midterm, the site said it would let us know by the 15th?

Anonymous said...

So the equation 6.11 of page 192, has H2SO4 over the arrow, would that imply that H2SO4 is a catalyst?

Anonymous said...

So the reason why cis and trans don't occur on alkynes is due to the fact that carbons can only have 4 bonds therefore we cannot set up cis and trans?

Scott McIndoe said...

827: none of it
830: yes
944: bond angle is 180 and only one substituent either side of the triple bond

Anonymous said...

The question from the homework assignment "Arrange substances Ga, Ne, and Br2 in order of increasing boiling point." says the answer is Ne, Br2, Ga. Why is that?

Scott McIndoe said...

London dispersion forces are weaker than metallic bonding. London dispersion forces are stronger for molecules with more electrons.

Anonymous said...

can aromatic rings be defined as alkene/alkyne?

RobinT said...

Aromatic rings are not considered alkenes, or alkynes. Their reactivity differs from alkenes and alkynes.

Anonymous said...

For the final exam, do we need to know the systematic and common names?

Scott McIndoe said...

You need to know systematic names, yes. Common names, no (except for perhaps some *really* common ones. Like "water").

Anonymous said...

In section 6.4 in the course notes we wrote "chain numbered so the double bond always gets the smallest possible number"

I found this example on mastering chemistry:
http://session.masteringchemistry.com/problemAsset/1259730/6/c.JPG

The question simply asks for the name. Mastering chemistry says the answer is cis-6-methyl-3-octene.
Why is it not cis-3-methyl-5-octene?
Thanks

Anonymous said...

I think there is a mistake at the top of page 76 in the course notes. I think the double bond in the molecule shown should be a triple bond. Is this correct?

RobinT said...

10:00: In mastering chemistry they followed the same rule that you quoted. The molecule is named so that the double bond is at the lowest numbered carbon that it can be at and in this case it is 3, thus 3-octene. When numbering starts on that side of the molecule to get to 3-octene the methyl is located at carbon 6, thus: cis-6-methyl-3-octene.

10:01: yes there is a triple bond, the molecule is 4-methyl-2-pentyne.

Anonymous said...

I had a question about #6 on the quiz from yesterday (Nov.27th). it asks: The formation of aspirin by reacting salicylic acid with acetic acid is a __________ reaction.

I know the answer is a condensation reaction, but i'm not sure how they arrived at that answer.

Anonymous said...

In the textbook on page 191 in the bottom left corner of the closer look text box it says "Because the rate-determining step involves both the alkene and the acid, the rate law for the reaction is second order, first order in the alkene and first order in HBr:"

Could you explain what that means and what the diagram beneath it means?

RobinT said...

1235:Because water is given off.
1134:The reaction being second order, first order to each of alkene and HBr means that the reaction rate will depend on both the alkene concentration and the concentration of HBr. I am not sure which diagram you are referring to.

Anonymous said...

I don't understand how to construct isomers, whether they were structural or geometric.

Scott McIndoe said...

Isomers are simply the same collection of atoms arranged in different ways. So say I asked you to draw all possible isomers of C4H10; you could draw butane or 2-mthylpropane - all other options you will not be able to draw sensible Lewis structures for. If I said draw all possible isomers of C4H8, you would draw cyclobutane, 1-butene, cis-2-butene or trans-2-butene.

Anonymous said...

Is a substance more acidic if its Pka is lower? (eg: Substance A has Pka~15 & substance B has Pka~10, which one is more acidic)?

Anonymous said...

What do we have to know exactly for Biochemistry, chemical biology, & medicinal biology for the final exam? (Just definitions, or the names of certain substances related to each one)?

Sarah said...

On Problem 2 - Naming Organic Molecules I in the video answers, isn't the second compound supposed to be 4-methyl-trans-2-pentene? (there isn't the 'trans' part in the answer)

Scott McIndoe said...

420: yes
443: Nothing. Dr Hof didn't give us a question to ask (and I think he told you he wouldn't in class).
600: Yes, you're right! Sorry about that.

Anonymous said...

Will we be expected to know the common names of organic compounds, or is it sufficient to be able to systematically name them? ie. Ethanamide vs. acetamide

Anonymous said...

Aaaand I see that question was answered above. My apologies.

Anonymous said...

In one of the MC questions, it says: Give the structural formula for an aldehyde that is an isomer of acetone.

How can we solve this?

(PS: Sorry, I posted this question in the wrong heading [Midterm Practice]).

Anonymous said...

How can we draw the structure of the compound formed during a condensation reaction between benzoic acid and ethanol?

Anonymous said...

How can we identify if a molecule is chiral or not?

Anonymous said...

On MasteringChemistry, a question said: An organic compound is analyzed and found to contain 66.7% carbon, 11.2% hydrogen, and 22.1% oxygen by mass. The compound boils at 79.6 ∘C. At 100 ∘C and 0.970 atm, the vapor has a density of 2.28 g/L. The compound has a carbonyl group and cannot be oxidized to a carboxylic acid. Suggest a structure for the compound.


The correct answer was 2-butanone, but I'm not sure how they got it..

Anonymous said...

is there an easy way to determine how many isomers a molecule has, or is drawing them all out and counting them the only way?

Scott McIndoe said...

305, 307: thanks
614: I answered it there
632: it's an ester, C6H5COOC2H5
644: Look for C with 4 different groups attached
657: %ages give you proportions of C:H:O. Non-oxidizable carbonyl means its a ketone. There is only one butanone.

Anonymous said...

Do we have to know the names of polymers (i.e. polyurethane, polystyrene, polyvinyl chloride, polycarbonate, polyethylene terephthalate) and their structures, for the final exam?

Anonymous said...

It seems as though, you skipped the question at 910, could you please answer it? thanks

Scott McIndoe said...

Oops, so I did, sorry. No, there is no easy way - just draw them out and carefully compare them to check you haven't drawn the same one twice.

Anonymous said...

are we just going to be tested about the material went through in class for organic chemistry?

Anonymous said...

If I want to give the iupac name of ethylene glycol is it 1,2-ethandiol or ethane-1,2-diol?

Anonymous said...

For #2 in the chapter 6 questions in the lecture book, how come trans isn't used when naming the second alkene?

Scott McIndoe said...

948: no, the whole course
948: ethane-1,2-diol
1039: It should have been. Argh! Sorry.

Anonymous said...

For Problem 2 In the Problem Solving (You Tube Videos) wouldn't the 4-methyl-2-pentene be trans-4-methyl-2-pentene?

Scott McIndoe said...

Yes.