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Joyce W.
Berkeley tutor with 3 years experience
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Organic Chemistry
TutorMe
Question:

What are similarities and differences between SN1 and SN2 reactions?

Joyce W.
Answer:

Similarities: they accomplish the same goal of replacing a leaving group with a nucleophile. Differences: 1) SN1 takes 2 steps. SN2 takes 1 step. 2) Speed of SN1 relies on leaving group ability, SN2 relies on strength of nucleophile. 3) Product of SN1 is a mixture of 2 stereoisomers, SN2 is stereoselective with an umbrella flip. 4) SN1 is preferred in polar aprotic solvents, SN2 in polar protic solvents.

Chemistry
TutorMe
Question:

What is the photoelectric effect? What happens when you increase the intensity of the light? What happens when you increase the wavelength of the light?

Joyce W.
Answer:

You know that one carnival game with the hammer that you slam in order to ring the bell (strongman). Well the photoelectric effect is exactly like that! Say you have 3 homies conveniently named Red, Green, and Blue. Red is a tall skinny wimp, green is your average joe, and blue is super buff but super short. They all take turns trying to swing the hammer strong enough so that they can ring the bell. Red goes first and isn't strong enough to ring the bell. Green goes next and he just BARELY hits it. Blue is last and hits it easily. Red gets frustrated and decides to hit it a bunch more times but he still can't get the bell to ring (sad life). This is the same thing with the photoelectric effect. The whole goal is to shoot some photons at a metal in order to eject an electron (i.e. swing a hammer to ring a bell). In order to eject an electron, you must overcome the minimum work function (i.e. swing the hammer hard enough to ring the bell). Shorter wavelengths have higher energy. Within the visible spectrum, red light has the longest wavelength but the lowest amount of energy. Green has a moderate wavelength and amount of energy. Finally, blue has a short wavelength but is higher in energy. Therefore increasing the wavelength, decreases the energy, until you can no longer overcome the minimum energy needed to eject an electron (aka anything weaker than green isn't going to be able to ring the bell). Increasing the intensity means that you are shooting more photons (i.e. swinging the hammer more). No matter how much you increase the intensity of a weak laser, you will never be able to eject an electron (i.e. no matter how many times red swings that hammer, he will never be able to ring the bell because he is too weak). [There's more to this explanation if you're interested!]

Biochemistry
TutorMe
Question:

What's a useful way to remember all of the amino acids?

Joyce W.
Answer:

I typically use an acronym to group them together by category as well as by similarity in structure: Gav-limp Stan-qc Freeway Hecka-ready nonpolar: GAVLIMP polar: STNQC aromatic: FWY charged: HKRDE

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