For students taking Chemistry 101 at the University of Victoria in the Fall 2013 term.
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.
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?
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.
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.
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.
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?
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?
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.
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.
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?
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.
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.
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)?
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)
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.
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
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..
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.
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?
49 comments:
will midterm #2 be just on chapters 4 and 5?
Yes, but it will draw on what you learned in earlier chapters, too.
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?
Yes, through London dispersion forces.
Is lecture help in Elliot still available Monday to Wednesday?
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.
The drop in centre in Elliot is closed Nov 11 to Nov 15.
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
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.
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.
Will a portion of chapter 6 be covered on the midterm, the site said it would let us know by the 15th?
So the equation 6.11 of page 192, has H2SO4 over the arrow, would that imply that H2SO4 is a catalyst?
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?
827: none of it
830: yes
944: bond angle is 180 and only one substituent either side of the triple bond
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?
London dispersion forces are weaker than metallic bonding. London dispersion forces are stronger for molecules with more electrons.
can aromatic rings be defined as alkene/alkyne?
Aromatic rings are not considered alkenes, or alkynes. Their reactivity differs from alkenes and alkynes.
For the final exam, do we need to know the systematic and common names?
You need to know systematic names, yes. Common names, no (except for perhaps some *really* common ones. Like "water").
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
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?
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.
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.
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?
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.
I don't understand how to construct isomers, whether they were structural or geometric.
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.
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)?
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)?
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)
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.
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
Aaaand I see that question was answered above. My apologies.
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]).
How can we draw the structure of the compound formed during a condensation reaction between benzoic acid and ethanol?
How can we identify if a molecule is chiral or not?
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..
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?
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.
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?
It seems as though, you skipped the question at 910, could you please answer it? thanks
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.
are we just going to be tested about the material went through in class for organic chemistry?
If I want to give the iupac name of ethylene glycol is it 1,2-ethandiol or ethane-1,2-diol?
For #2 in the chapter 6 questions in the lecture book, how come trans isn't used when naming the second alkene?
948: no, the whole course
948: ethane-1,2-diol
1039: It should have been. Argh! Sorry.
For Problem 2 In the Problem Solving (You Tube Videos) wouldn't the 4-methyl-2-pentene be trans-4-methyl-2-pentene?
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