Chemistry

Page 1

CHAPTER #1: STRUCTURE and BONDING

ORGANIC CHEMISTRY

DEFINITIONS AND HISTORY

In the early 1800’s “organic molecules” came from an organism.

In 1828 Frederich Wohler synthesized urea (natural, organic) from ammonium cyanate (inorganic). Urea had never before been made “…without thereby needing to have kidneys…”

Elements in Human Body Elements in Dry Human Oxygen 65% Carbon 62% Carbon 18% Nitrogen 11%

Hydrogen 10% Oxygen 9% Nitrogen 3% Hydrogen 6% Calcium 1.5% Calcium 5%

C NOH N

H

H

H

C

O

N NH

H

H

H

heat

ammonium cyanate urea

Page 2

WHY CARBON?

ORGANIC CHEMISTRY TOPICS

Molecular Structure and Atomic Groupings

Ethyl alcohol (“alcohol”) Dimethyl ether (propellant)

Chemical Reactions

H C

H

H

C

H

H

O H H C

H

H

O C H

H

H

C

C C

C

C C C

O

O

O H

H

H

H

H

H

C

C C

C

C C C

O

O

O

H

H

H

H

H C O C

H

H H

C C O

O C C

O

H

H H

H

H H

salicylic acid acetylsalicylic acid

Page 3

LEWIS STRUCTURES

METHOD

1. Sum the valence electrons.

For each negative charge ____________________, for each positive charge ____________________.

2. Draw the skeleton (for complicated structures this may be given).

3. Use the valence electrons to give all atoms an octet (8 e–), except hydrogen which should have a duet (2 e–).

EXAMPLES

CH2O (Formaldehyde) CH3NH–

CH2NH2– CH2NH2+

NaCN (sodium cyanide)

Page 4

FORMAL CHARGE

METHOD

For each element apply this formula:

Formal Charge = (Valence electrons) – (Electrons “owned” by the element)

HONC PRINCIPLE

When neutral… H makes O makes N makes C makes

Anion Neutral Cation

HCONH– NO3–

+ H C

H

O H

H C

O

N H O N

O

O

Heme unit in hemoglobin

Page 5

RESONANCE STRUCTURES

REVIEW

CHO2–

Bond Lengths1

Labrador Poodle Carbonate bond lengths2

1 Allen, F.H., Kennard, O., J. Chem. Soc., Perkin Trans., 2, 1987, S1-S19 (follows p. 1914) 2 Solomons, G., Fryhle, C.B., Organic Chemistry, 8th ed., Wiley, 2004, pp. 15

H C

O

O

C

O

C

O H C

O

O

O

C O O

Page 6

RESONANCE

REASONABLE RESONANCE STRUCTURES

In “reasonable” resonance structures,

MAJOR AND MINOR CONTRIBUTORS

To follow are rules (in order of importance) for determining the major resonance contributor for a compound:

1. A resonance structure where all atoms have an octet contributes more than a resonance structure that lacks an octet (most important “rule”).

Electrostatic potential energy diagrams (color-coding electron density)3

3 Electrostatic potential energy diagrams in this chapter were generated by Lisa Nichols using WebMO, thanks to the Institute for Chemical Literacy through Computational Science.

C O C O OC O

C HH

O

C HH

C N

H

H H

H

H F

Page 7

2. A neutral resonance structure contributes more than one with charge, especially separated charge.

3. When all structures have octets and charge, the greatest contributor has the charge on the element with the appropriate electronegativity. a. A negative charge is best situated on the __________ electronegative atom.

b. A positive charge is best situated on the __________ electronegative atom.

H C

O

N

H

H

H C

O

N H

H C

O

N H

H

H

Page 8

MORE EXAMPLES

Draw all resonance structures, then rank in order from most important to least important to the overall resonance hybrid. Explain your answer.

(There are 5 total, but only draw 2 more)

RESONANCE AND ENERGY

C C

C N

H

H

H

H

H

C

C N

C

C

H

H H

H

H C

O

O H C

O

O H C

H

O

H

vs.

H C

O

O H C

O

O H C

O

C H C

O

CH

H

H

H

vs.

Page 9

COMMON POLYATOMIC IONS

MOLECULAR SHAPE (VSEPR)

e– groups around central atom

e– geometry

bond angles

central atom hybridization

O N

O

OO

N O O

O N

O

O

O N

O O N

O

O P

O

O

O

O

P O

O

O OP

O

O

O

O

PO

O

O

O C

O

OO

C O O

O C

O

O

O Mn

O

O

O

O

Mn O

O

O OMn

O

O

O

O

MnO

O

O

Page 10

HYBRIDIZATION AND ORBITAL DIAGRAMS

VALENCE BOND THEORY

Bonding in F2

sp3 HYBRIDIZATION

Ammonia angles4

4 Jones, M., Fleming, S.A., Organic Chemistry, 4th ed., Norton, 2010, pp. 252

H N

H

H orbital

diagram

H C

H

H

H

Page 11

sp2 HYBRIDIZATION

Ethylene angles5

sp HYBRIDIZATION

Total σ bonds: ________ π bonds: ________

5 Jones, M., Fleming, S.A., Organic Chemistry, 4th ed., Norton, 2010, pp. 46

O C H

C H

H H

H C

H

H

C C

C C H

H H

H

Page 12

SHAPE AND HYBRIDIZATION SUMMARY

1. Assuming hybridization of the oxygen atom, lone pair A is in what type of orbital?

2. List the orbitals on both carbon atoms used to form the sigma bond labeled B.

3. Estimate bond angle C.

4. List the orbitals on carbon and oxygen atoms used to form the σ and π bond in D. σ:

π:

5. What is the electron geometry of the atom labeled E?

6. What is the hybridization of the nitrogen atom?

7. List the orbitals used to make the σ bond labeled F.

C C C

H

H

C

H

H

C

O

H

C

H

H

OH

N

O

A

B C

D

E F

Order now and get 10% discount on all orders above $50 now!!The professional are ready and willing handle your assignment.

ORDER NOW »»