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THE U / Chemistry / CHEM 2310 / It is known as "electron lover". what is it?

It is known as "electron lover". what is it?

It is known as "electron lover". what is it?

Description

School: University of Utah
Department: Chemistry
Course: Organic Chemistry I
Professor: Peter stang
Term: Fall 2016
Tags: Chemistry
Cost: 50
Name: Chem 2310 Midterm 1 Study Guide
Description: Here is the Midterm 1 Study Guide! It covers the seven topics that will be on our exam: resonance, hybridization, acidity and basicity, electrophiles and nucleophiles, functional groups, Infrared spectroscopy, and Carbon 13 NMR.
Uploaded: 02/02/2016
5 Pages 57 Views 1 Unlocks
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Friday, February 5, 2016 1:18 PM Midterm 1 Study Guide


It is known as "electron lover". what is it?



1. Resonance

Resonance structures are electrons moving around an atom. This is facilitated by double  bonds, and electronegative atoms (such as O) who are willing to take a charge. •

No molecule with resonance structures is completely one or the other. The sum of all the  resonance structures is the most true bond structure of the molecule • Full headed arrows are used to show the movement of a pair of electrons in the structure• Half headed are used to show the movement of a single pair of electrons in the structure•

Double headed arrows are used between the structure to show that the resonance goes both ways


What are the common bases?



Don't forget about the age old question of What are the types of statements and how they differ?

2. Hybridization

• Each carbon has 1 s orbital and 3 p orbitals to bond with other elements.

4 bonds around C

 3 bonds around C

Like CH4

Like CH2=CH2

Like CH≡CH

 

Sp3hybridization

 Sp2hybridization 

  Sp hybridization

75% s character

 ~33% s character

 50% s character


Define resonance.



Don't forget about the age old question of What is the document where you write your code that can be saved?

 2 bonds around C

  

•The conjugate base ends up with a 1- charge from where it started (meaning that for both,  

  

 

• Any connection between a two hybridized orbitals makes a sigma (ߪ (bond

○ The leftover p orbitals from any two carbons bond and create a pi (ߨ (bond

• More s character in the bond means a shorter and a stronger bond 3. Acidity

Donates

 Accepts

e-

Lewis base

 

p+

Bronsted acid

 

Don't forget about the age old question of Which person is not counted as unemployed?

In both cases

 

 Lewis acid  Bronsted base

The conjugate acid ends up with 1+ charge from where it started (meaning that for both, the base gains a positive charge)

○ Base gains positive (b and p are similar letters)

the acid gains a negative charge)

The smaller the pKa, the more acidic the chemical

Trends that affect acidity (in order of the most to least important)  Organic Chemistry Page 1

Trends that affect acidity (in order of the most to least important)

1) Element effect

The larger the atom holding the negative charge, the more acidic the chemical 2) Inductive effect

If there are electronegative atoms connected (in proximity) to the atom containing the

negative charge, the chemical is more acidic

3) Resonance effect

If there are possible resonance structures which move the negative charge around, the We also discuss several other topics like What is the inverse of zero?

chemical is more acidic

4) Hybridization effect

The larger the s character in the hybridized bonds, the stronger the acid

Common acids and bases:

Acids:

• Formic acid: CHOOH

• Acetic acid: CH3COOH

• Methanesulfonic acid: CH3S(O)2OH

• Toluenesulfonic acid: CH3(benzene ring)S(O)2OH • Sulfuric acid: HOS(O2)OH

Common bases

• Derived from alcohol (-OH)

Methoxide ion: (CH3O- + Na+(or Li+ ○ )) We also discuss several other topics like How do dna chains interact with each other?
We also discuss several other topics like How to solve limits?

Ethoxide ion: (CH3CH2O- + Na+(or Li+ ○ ))

t-Butoxide: (CH3)CO- ○

• Derived from nitrogen : ammonia and amines (NH3)

Li+ NH2- ○

Sodamide: Na+ NH2- ○

• Derived from H2

Sodium Hydride: Na+ H- ○

To remember the direction of trends on the periodic table:

4. Electrophilicity and Nucleophilicity

Nucleophile

"nucleus lover" Because nuclei are positively charged, you know that the nucleophile will have a free negative charge to pull it to the nucleus (opposites attract)

• A nucleophile is a molecule that donates an electron pair to form a chemical bond. •

Any molecule with at least one pi bond or any free pairs of electrons (such as the two lone  pairs on any -OH group) can act as a nucleophile

• Lewis Base

Electrophile

• "electron lover" Because it loves negative charges, it will have a positive charge to pull it   Organic Chemistry Page 2

"electron lover" Because it loves negative charges, it will have a positive charge to pull it  toward the electrons of a nucleophile. It can also be a neutral atom with vacant orbitals that want electrons to fill it.

• High electronegativity means a good electrophile, in general.

5. Functional groups

(ring of C)

 Aromatic

R-OH

 Alcohol

R-NH2

Amine

 

R-X

 Alkyl halide

R-O-R'

 Ether

 (I remember this because there is an alkyl group on "ether" side of the O)

R-S-R'

 Sulfide

R-CH=O

 Aldehyde

R2-C=O

 Ketone

R-C(OH)=O

acid

 Ester Perfume - the concentration of ether in perfume matters a lot

 Carboxylic  

 

R-C(O)-O-R

R-C(X)=O

 Acid halide

R

C(NH2)=O

Amide

 The H attached to the N can be substituted with other alkyl

groups

C=C

 Alkene

C≡C

 Alkyne

 

You most likely don't have to memorize all of these groups and their names. Just be familiar  with them and their properties:

Intermolecular Interactions (from strongest to weakest)

The stronger the interactions between functional groups, the higher the boiling and melting points1) Ionic

If the element dissociates, ionic bonding is present.

Extremely strong (think of the high melting point of table salt, which is a very stable  solid)

2) Hydrogen Bonding

A form of dipole-dipole bonding that happens when a hydrogen is attached to an  electronegative atom that gives the H a positive dipole moment

i.e. any -OH group

Any long chain of carbons get in the way of hydrogen bonding, and hinder it somewhat

3) Dipole

All functional groups have this to some degree, no exception When there is a difference in electronegativity, there is a 'dipole moment' which causes

some atoms in the molecule to be more or less negative. The partial negative atoms  attract the partial positive atoms in other elements

4) Van der Waals

Every single molecule has this, no exceptions

Exceedingly weak

 Organic Chemistry Page 3

6. Infrared Spectroscopy

When electromagnetic radiation is shot at a chemical, some wavelengths are absorbed as  energy to bend or stretch certain bonds. Using those energies absorbed, one can tell what  kind of bond and what groups are present.

The wavelength is measured by wavenumber (cm-1), which is inversely proportional to the  wavelength

• Higher frequency = higher energy = higher wavenumber

Csp3-H

Csp2-H

Csp-H

3000-28503150-30003300

Strong

Medium

 

Medium

 

 

C≡C

 2250 Medium

C=C

 1650 Medium

(benzene ring)

 1600, 1500

 Medium 

C=N

 2250 Medium

N-H

 3500-3200 Medium

C=O

 ~1700 Strong

O-H

 3600-3200 Strong (low) and broad peak

 

 

 

 

 

 

 

 

 

 

 

 

Pay attention to symmetric or asymmetric stretching (like for the two H on a normal NH2bond which gives two signals instead of just one.

Any symmetric atom (i.e. O=C=O) will not show the functional group because the two  frequencies of the bonds "bouncing" will cancel each other out ○ If there is a signal, that group is present for sure ○ If there is not a signal, the group could still be there

4000

 2500

 2000

 1500

Bonds to HydrogenC-H

O-H

N-H

Triple

bonds

C≡C

C≡N

Double  

bonds

C=C

 

C=O

 

C=N

 

Single

 

Bonds

C-C

C-O

 

C-N

C-X

(lighter

atoms, so higher

frequency)

(stronger bonds,

 

higher

 

frequency)

 

(fingerprint region)

7. Carbon 13 NMR

 400

 

 

 

 

 

 

Nuclei have natural magnetic fields, which are aligned along an outside magnetic force and  then measured.

• Lower energy nucleus = aligned in the same direction as the outside force (up)  Organic Chemistry Page 4

• Lower energy nucleus = aligned in the same direction as the outside force (up) • Higher energy = aligned against the outside force (down)

• Downfield is from right to left, going to larger numbers; also called a 'chemical shift' 13 • C is used for NMR

• There are at least as many carbons present as there are signals, sometimes more

• Exactly similar carbons give only a single signal

 Organic Chemistry Page 5

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