Cerberus

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List em and give tips on how to improve them:

Stereochemistry - I just cannot seem to get this. I'm not quite sure how I aced ochem.

Harmonic Motion - dont know why I have trouble with this:confused: :confused:

Phase Diagrams: triple point whaaa??? :confused:

Calorimetry: just never liked it

mirrors/lenses: only slightly a problem


I'd say my biggie right now is Stereochem, everything else I know *fairly* well. I have looked at my ochem book yet it still doesnt click. How can i rectify this?
 

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In my ochem class, we were all required to buy those dinky plastic molecule kits. I laughed at the time, but they were really helpful. Put 4 different colors on a carbon, make the mirror image, and try to superimpose them. Each thing on the carbon can represent a whole group. We got to use the kits during tests (as if we had time to build anything during the test, lol), but even as something to help your mind wrap around the concept, highly recommended. And you'll be able to start rotating pictures in your head too. : )

Fisher projections are kinda fun I used to think.
 

jhk43

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Weaknesses:

Evolution and Taxonomy. (so boring, still havent reviewed it)

Enzymes.


Carbohydrate Fischer projections (cant keep track of that damn nucleophile carbon)
 

confewshz

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Originally posted by Cerberus
List em and give tips on how to improve them:

Stereochemistry - I just cannot seem to get this. I'm not quite sure how I aced ochem.

Harmonic Motion - dont know why I have trouble with this:confused: :confused:

Phase Diagrams: triple point whaaa??? :confused:

Calorimetry: just never liked it

mirrors/lenses: only slightly a problem


I'd say my biggie right now is Stereochem, everything else I know *fairly* well. I have looked at my ochem book yet it still doesnt click. How can i rectify this?

Cerberus, the best thing that helped me understand Stereochemistry were ball n stick models. You can build a simple ethane molecule and learn the orientations in 3-D. Im a visual learner though, so thats probably why they helped me so much. They sell them at Amazon.com if you are interested. Follow this link. Hope this helps
 
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kohlmayberrry

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Answer to all your problems: Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice
 

confewshz

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Originally posted by kohlmayberrry
Answer to all your problems: Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice Practice

I second that :)
 

Cerberus

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Man, stereochem pwns me:( I dont know why either:( I cannot figure out one of the examples in my book, i stared at it for about an hour before giving up out of frustration. Maybe I will scan it later and post it.
 

Cerberus

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I took the BS section of the Berkely Review Exam VI and DAMN that was hard. There were 2 passages where I missed 80% of the questions (I did fairly well aside from those 2 passages but damn!):wow: :wow:

My overall scaled score for BS was a 10. I am gonna take the PS section in a few minutes and see how I do on it.
 
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confewshz

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Originally posted by Cerberus
There were 2 passages where I missed 80% of the questions (I did fairly well aside from those 2 passages but damn!):wow: :wow:
Maybe those 2 passages were the experimental passages :laugh:
 

Cerberus

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Ok, here she is.

chem.gif



Now I see how the original 2R,3R config was reached (below drawing)
chem2.gif



However, I thought when the lowest priority substituent (Hydrogen) was on the horizontal line it reversed configuration (i.e. R becomes S and S becomes R). In fact, on the page before this drawing it says "if the lowest priority is on a horizontal bond, the anwser is Horribly wrong". What am I doing wrong here?

btw - thanks for telling me about this program confuscious:love:
 

confewshz

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Cerb, we cant see the pix you posted. You put them on a secure web server that requires login. I dont know how big they are, but try uploading them to your post instead.
 

confewshz

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Originally posted by farleyisgod
In my mind, I was pronouncing it "Confwayza" or something completely idiotic until I read this.

:(
LMAO, farleyisgod, you're not the only one whose butchered my nick. :)
 

JDAD

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This doesn't help you cereb, but is anyone else have problems with the actual math on the ps section.

I can do the formula, and i know what to do, but i can't calculate it out without the calculator. Any quick fixes?
 

farley is god

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Originally posted by jarrod_dale
This doesn't help you cereb, but is anyone else have problems with the actual math on the ps section.

I can do the formula, and i know what to do, but i can't calculate it out without the calculator. Any quick fixes?

There's an EK book that discusses Math and Verbal strategies. I only glanced over the Math part, so someone else might be able to better tell you how useful it is.
 

JDAD

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If the lowest priority group (# 4) is on a horizontal bond, then the structure as drawn has the lowest priority group oriented toward you. Therefore, your perspective on the structure is the opposite of what you need to assign the configuration directly. In a case like this, draw a circle to connect the groups with priorities 1 to 2 to 3 as before but now reverse the configuration that you get from directly reading the Fischer projection.
 

UCLAstudent

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Cerb, if you imagine that molecule in 3-D, both the OH and the H stick out at you, while the two vertical groups point back. It's true that you have to reverse configuration when the H group is pointing at you (from R to S), but when they draw the molecule out like that for you, I find it much easier to rotate the molecule in my head and put the H pointing backward. That way, you don't have to reverse anything.

Keep in mind that it is tetrahedral. Looking at carbon two only, draw it with wedges for H and OH, and dashes for COOH and the big R group. Rotate it (in your head or on paper... I worked it out on paper just now) so that OH, R, and H are all pointing AT YOU while COOH is on a dash in the back. The way I drew it, I have OH on top, R on the right, and H on the left (all on wedges). From there, you only need to put the H in the back. When you rotate to get H in the back, you should end up with COOH on top, OH on left, and R on the right, all on wedges pointing at you. Priority is 1 for OH, 2 for COOH, and 3 for R... which results in R configuration.

I am sorry if this is super confusing. It's hard to explain without showing you my drawing. I hope it helps!
 

JDAD

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i have the ek book, it helps, but i am still having problems.

the other day, i couldn't find the distance an object would fall if dropped out of a plane with a horizantal velocity of 100m/s and it was allowed to fall for .001 seconds. (no air resistance)

I know that the horizantal velocity has nothing to do with it, and i need to use x=1/2at(squared)

a must be ~10m/s2

then all i have to do is (0.5)(10)(.001)squared.


How do i square .001?
 

Cerberus

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Originally posted by jarrod_dale
i have the ek book, it helps, but i am still having problems.

the other day, i couldn't find the distance an object would fall if dropped out of a plane with a horizantal velocity of 100m/s and it was allowed to fall for .001 seconds. (no air resistance)

I know that the horizantal velocity has nothing to do with it, and i need to use x=1/2at(squared)

a must be ~10m/s2

then all i have to do is (0.5)(10)(.001)squared.


How do i square .001?

right everything in scientific notation. The you get:

5*10^-1 *10^1*(1*10^-3)^2

Now it might be easier for you to think of it like this now:
5*x^-1*x*(x^-3)^2
which easily reduces to:
5*1*(x^(-3*2)) = 5*(x^-6) = 5*10^-6

Hope that makes it clearer:)
 

JDAD

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thanks for that tip.

i have always avioded scientific notation because it confused me, that alone is going to add at least 3 points onto my ps score.

34 here i come (at least, that is where i want to go)

thanks guys.
 
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