Nucleophile vs Electrophile

Nucleophile: is negative so is attracted to positive parts of molecules
has an electron pair it can donate
example reaction: (OH)-ion added to halogenoalkane, displacing halide ion to for alcohol. 


Electrophile: is positive so is attracted to negative parts of molecules, like a double bond (electron lover)
wants to accept an electron pair 
example reaction: Hydrogen bromide (H is delta +ve due to dipolar bond) added to alkene (with double bond) to form halogenoalkane. 

Substitution Nucleophilic Reactions (SN1/SN2)
All in one place:

I’m trying to read about nucleophilic substitutions but I laugh everytime the phrase “back-side attack” comes up. Which is really, really often.

Why am I a thirteen year old boy?

Organic Chemistry I: Do I substitute the damn thing or eliminate?

Let’s hold hands so I can grab for your wallet and run. But you’re holding my hand. Damn it. Let go.

Let’s step by step this bad boy. Quick Fix #2:

1. Is your leaving group attached to a methyl? If yes, SN2

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2. If not, is the nucleophile a strong base? 

A. If yes, THINK ELIMINATION. THINK PROTONATION OF BETA HYDROGEN. is it a bulky base?

If yes: 

  • E2with the less stable alkene as the major product (anti-Zaitsev) 

If not:

  • Is the leaving group attached to a secondary or tertiary carbon? If yes - > E2, with the more stable being the major product (Zaitsev). 
  • If it’s attached to a primary carbon? Then it’s SN2

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B. If it’s not a strong base, what kind of carbon is the leaving group attached to?

  • If it is a tertiary carbon, then SN1
  • If it’s an unhindered primary or secondary carbon, SN2
  • If it’s a hindered secondary carbon, or a secondary benzylic or allylic carbon, it can go both ways: 
  • Is there a good nucleophile? If yes -> SN2. If no -> SN1

_________________________________________________________________

Dealing with alcohols

They do shit differently. 

1. Is a HX being used?

If yes, is the leaving group attached to a methyl or primary unhindered carbon? SN2

Primary hindered or secondary unhindered? BOTH SN1 and SN2

Secondary hindered or tertiary? SN1

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2. Is a HCI/ZnCl2 being used?

If yes:

  • Is the leaving group attached to a methyl? If so - SN2; if not, SN1

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3. Is H2SO4 or H3PO4 with heat used?

If yes:

  • Is the leaving group attached to a methyl or primary unhindered? If yes, SN2 (ketone)
  • If not, E1 (alkene) 

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4. Is a strong base used?

LOL THAT JUST MEANS YOU JUST DEPROTONATED YOUR SUBSTRATE. OOPS. 

5. Is a halide used?

LOL NO REACTION

Random thoughts from Organic Chemistry

You know you are getting into your orgo homework when you have to write out the steps of an SN1 reaction and your headings include gems like:

CARBOCATION POWERS ACTIVATE!

OH NO! NUCLEOPHILE ATTACK! TO YOUR BATTLE STATIONS CAROBCATIONS!

THE REVENGE OF THE DEPROTONATION! YOU CAN HAVE OUR CARBOCATION BUT WE SHALL STEAL YOUR PROTON! WHAT ARE YOU GOING TO DO ABOUT IT?

batmandeh said:

Ugh, sorry I can’t be of assistance, but fist bump of solidarity from a fellow libarts jackass who took astronomy.

HIGH FIVE, PAL. we are legion, and we are terrible.

fromtheshoresof said

for organic chemistry you could ask about chair conformations, electrophiles, nucleophiles, or chirality. for biology you could ask about dna replication or protein synthesis?

wwwwwouulllld any one of those single chemistry concepts that mean vague things to me be for any reason excluded from a college midterm? lik just as a matter of teaching a college level syllabus?

haise-kaneki said:

this if for the pickup line meme thing "I wish I were adenine because then I could get paired with U" "Let's do a Sn2 reaction, ill be the nucleophile and ur clothes can be the leaving group" this was really dirty im sry i cant thats it

nah son | maybe | HELL YES
These are my fave pickup lines.

studies ochem with nam

nam: okay so think nucleophile…. think nucleus! what’s inside of a nucle —

me: DNA 

nam: nucleus

me: CHROMOSOMES AND DNA

nam: …of an atom tina

me: ….protons…….

Substitution Nucleophilic Badassery p2 - THE DATA

For my fellow premed perverts who are currently dying in Organic Chemistry and are going through hell SN1/SN2. 

Let’s make sense of this shit. 

DATA BEFORE HYPOTHESIS

Remember when the professor started talking about data and results and you were like WTF BBQSAUCEANDABISCUITWHAT? Shit happened, we got data, and then we have to explain for it. Because chemistry. 3 things to remember about the data that was collected AFTER substitution reactions:

1.  The electrophile (or the substrate)

image

WITH THE FIRST REACTION, less steric hindrance substrates HAVE FASTER REACTION RATES, BUT IN THE SECOND REACTION, the MORE steric hindrance there is in the substrate,THE FASTER THE REACTION RATE IS. HUH, OK. BUT WHY THE FUCK?

2. The rate law

Because we can measure the rate of the reaction (1,2, shit it’s over 9000) we can fuck with the concentration of both the nucleophile AND the substrate and see if that changes the reaction rate at all. 

image

WITH THE FIRST REACTION, you double the concentration of the substrate while leaving the nucleophile the fuck alone, and you DOUBLE the reaction rate. Double the concentration of the nucleophile, and you DOUBLE the reaction rate. Double both concentration, and you increase the rate by four. Triple the concentration of both, and you increase it by nine times. Half the concentration of one of them, and you half the reaction rate. Mess with one, or both of these suckers, and you mess with the reaction rate. AWESOME. 

WITH THE SECOND REACTION, the rate ONLY changes when you fuck with the substrate. Touch the nucleophile, and NOTHING CHANGES. 

3. I’m bringing back stereochemistry

WE JUST FINISHED THE CHIRALITY CHAPTER, ARE YOU FOR SERIOUS? I THOUGHT WE WERE DONE WITH THAT SHIT. Look, that shit never goes away. Just DEAL okay?

Not only can we measure the rate, we can ALSO measure optimal rotation. (AHURHUR, STINGS DOESN’T IT, YEAH I’M BRINGING IT BACK.) Optimal rotation is based on stereochemistry (is it an isomer? If so, is it a constitutional or a stereoisomer? If so, are they identical or different? If so, are they enantiomers or diastereomers? AH GOOD TIMES).

image

WITH THE FIRST REACTION, you take a pure enantiomer compound, down that baby in a solvent, and you end up with a pure enantiomer compound - in reverse. If it started as a (2S)-2-bromo-butane, then the product will be a (2R)-butyl-cyanide.

WITH THE SECOND REACTION, we have a mixture of BOTH the same configuration and the reverse configuration. Because it’s a mixture, it’s a racemization (if have equal portions of both configurations)

THAT’S THE DATA. DATA BEFORE HYPOTHESIS. SO WHAT NOW HOME SKILLET?

They have to explain:

  1. How the bonds form and how they break
  2. The dependence on type of substrate
  3. The dependence on concentration
  4. The observations of stereochemistry

Think of hypothesis as “mechanisms”. And that’s what they are. Sounds less intimidating to think of them as hypothesis though… 

*images from Master Organic Chemistry

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