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CU DENVER / Chemistry / CHEM 3411 / What is the difference between nucleophiles and electrophiles?

What is the difference between nucleophiles and electrophiles?

What is the difference between nucleophiles and electrophiles?

Description

School: University of Colorado Denver
Department: Chemistry
Course: Organic Chemistry I
Professor: Doris kimbrough
Term: Fall 2016
Tags: Ochem, Newman, projections, and energydiagrams
Cost: 50
Name: Exam Study Guide for Exam two
Description: This study guide covers all of the topics that will be on exam two. This include the newman projections and energy diagrams.
Uploaded: 03/11/2018
8 Pages 50 Views 3 Unlocks
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O’Chem Exam Two Study Guide: Blank


What is the difference between nucleophiles and electrophiles?



I. Nucleophiles, Electrophiles, and Leaving Groups: definitions and identification in chemical reactions and using curved arrow formalism

II. Acid Base Chemistry

A. Definitions (Bronsted Lowry vs. Lewis), identifying in reactions

B. pKa and acid strength

C. Relative strengths of acids and their conjugate bases

D. Acid strength

1. Electronegativity

2. Atomic size

3. Sigma inductive effect

a) Distance from anion

b) Electronegativity

c) Number of electronegative groups

E. Pi resonance effect on strength of bases and availability of non bonding pairs III. Conformations of Alkanes and Cycloalkanes


What are the sigma inductive effects?



A. Newman projections and conformational analysis (staggered, eclipsed,gauche, anti, relative energies)

B. Cyclohexane chair forms

C. Interconversions

D. Axial and equatorial positions

E. Substituted cyclohexanes

1. Cis/trans/axial/equatorial structures for disubstituted and trisubstituted cyclohexanes and relative stabilities

IV. Alkenes

A. Addition reactions

1. Addition of HI,HBr and HCl (hydrohalogenation)

2. Carbocation stability (3o> 2o> 1o)

3. Regioselectivity (Markovnikov)

4. Addition of H2O in the presence of acid (hydration)

B. Mechanisms

1. Using curved arrow formalism to draw mechanisms


How is acid affected by the atomic size?



Don't forget about the age old question of What are the components of cytoskeleton?

2. Transition state energy and the Hammond Postulate

3. Drawing reaction energy diagrams

4. Carbocation rearrangement

O’Chem Exam Two Study Guide: Completed

V. Nucleophiles, Electrophiles, and Leaving Groups

Nucleophiles​: Nucleus loving usually has a negative charge and/or a lot of negative character, analogous to a Lewis Base.

Electrophiles:​ Usually has a positive charge and/or a lot of positive character. It is analogous to a lewis Acid.

Leaving Groups:​ Typically receives electrons from the breaking bond and “leaves” (the molecule) with that pair of electrons.

Ex: Image One 

*Nucleophile is at the bottom of the arrow, electrophile is at the top pointy part of the arrow, leaving group is what is left over and not in the reaction anymore

VI. Acid Base Chemistry

A. Definitions (Bronsted Lowry vs. Lewis), identifying in reactions

1. Bronsted Lowry Acid:​ proton donor

2. Bronsted Lowry Base:​ proton acceptor

*Acid - Base Conjugate pair differs by just ONE proton (acid has the extra proton, the one with the more hydrogen)*

3. Lewis Acid: electron pair acceptor

4. Lewis Base: electron pair donor (has the lone pair of electrons on it, to donate)

Ex: Image Two We also discuss several other topics like What is the largest lymphatic organ in the body?

B. pKa and acid strength

● Lower pKa, stronger acid, higher pKa weaker acid Don't forget about the age old question of What happens when someone experiences milk letdown reflex?
We also discuss several other topics like Which elements make a contract valid?

C. Relative strengths of acids and their conjugate bases

● Stronger acid, stronger conjugate base

D. Acid strength

1. Electronegativity: ability to attract e- density in a covalent bond

● The more electronegative the acid is the stronger it is.

2. Atomic size

● The larger the atom, the more acidic it is.

3. Sigma inductive effect

a) Distance from anion

● The closer it is to the anion the more acidic We also discuss several other topics like What are the benefits of sampling distribution?

b) Electronegativity

● The more electronegative the acid is the stronger it is.

c) Number of electronegative groups

● The more number of electronegative groups the more acidic

it is.

d) Pi resonance effect on strength of bases and availability of non

bonding pairs

● The delocalization of electron density enhances stability.

VII. Conformations of Alkanes and Cycloalkanes

A. Newman projections and conformational analysis (staggered, eclipsed,gauche, anti, relative energies)

Ex: Image three 

*eclipsed has higher energy than staggered (maximums), gauche is higher than anti (minimums)

B. Cyclohexane chair forms

C. Interconversions

D. Axial and equatorial positions

For B - D Example

Ex: Image #4 

E. Substituted cyclohexanes

1. Cis/trans/axial/equatorial structures for disubstituted and trisubstituted cyclohexanes and relative stabilities Don't forget about the age old question of What are the key differences between the stance of erasmus and ramus?

Ex: Image Five 

● Stability:

○ Higher electronegativity in equatorial positions

○ trans is more stable than cis for substituted cyclohexanes

VIII. Alkenes

A. Addition reactions

1. Addition of HI,HBr and HCl (hydrohalogenation)

● Step One: Electron pair from the pi bond are donated to the H+ of

the HBr (or HCl, HI) to

○ Forma new bond between C and H and

○ Leave behind a positive charge on the other carbon. This is

a carbocation (cation on the carbon that used to be in the

double bond that did NOT bond to H+)

● Step Two: Halide ion (Br-) reacts with electron deficient

carbocation to form a C-Br bond.

Ex: Image Six 

2. Carbocation stability

● 3o> 2o> 1o

3. Regioselectivity (Markovnikov)

● When more then one possible regioisomer is possible in a chemical

reaction, the one that is more would be the regioselective one.

● The one that forms is when the halogen is on the more substituted carbon.

4. Addition of H2O in the presence of acid (hydration)

● Step One: The alkene pi bond acts as a nucleophile and picks up a proton (H+) to form the most stable carbocation.

● Step Two: The water acts as a nucleophile and reacts at the

carbocation center.

● Step Three: The oxygen loses a proton to another water molecule to regenerate the H3O+.

Ex: Image Seven 

B. Mechanisms

1. Using curved arrow formalism to draw mechanisms

*See above addition reactions for example*

Ex: Image Six and Seven

2. Transition state energy and the Hammond Postulate

● The hammons postulate means that the transition state resembles that of the structure closest to it in free energy.

Ex: Image Eight 

3. Drawing reaction energy diagrams

Ex: Image Nine 

● Rate determining step: slowest elem. step

● Elementary step: one of the bond breaking/forming step

● Activation energy: energy for an elem. step

4. Carbocation rearrangement

● Carbocations can rearrange to form more stable carbocations Ex: Image Ten

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