Homework DUE Friday, 5 SeptHomework DUE Friday, 5 Sept

Problems in McMurry Problems in McMurry

1.24; 1.28; 1.31; 1.45; 1.46; 1.24; 1.28; 1.31; 1.45; 1.46; 1.471.47

=> (1.48—1.52 BONUS Problems)=> (1.48—1.52 BONUS Problems)

Organic Chemistry - 246AOrganic Chemistry - 246A

Hybridization of C, N & Osp3, sp2 & sp Bonding

Structure & Bonding (Chapter 1, pp 1—28)

• All of these atoms can be involved in single, double, and triple bonds• sp3 Orbitals make single bonds () 2 bonding e—

• sp2 Orbitals make double bonds ( + ) 4 bonding e—

• sp Orbitals make triple bonds ( + + ) 6 bonding e—

H3C NH2 H2C NH HC N

MethylAmine

MethyleneImine

HydrogenCyanide

H3C OH H2C O C O

Methanol(Methyl Alcohol)

Formaldehyde CarbonMonoxide

H3C CH3 H2C CH2 HC CH

Ethane Ethene(Ethylene)

Ethyne(Acetylene)

Ethylene H2C=CH2

• sp2 orbitals are in a plane with120° angles

• The remaining p orbital is 90° perpendicular to the plane containing the sp2 orbitals

90 120

• Two sp2 orbitals interact to form a double bond, one -bond + one -bond

Dihedral Rotation of Ethane

Ethane Rotation

0

0.5

1

1.5

2

2.5

3

3.5

4

-170 -150 -130 -110 -90 -70 -60 -40 -200 20 40 60 80 100 120 140 160 180

Rotation Angle

Energy (kJ/mol)

Energy

Dihedral Rotation of Ethylene

Ethylene Rotation

0

5

10

15

20

25

30

35

40

45

50

-170 -150 -130 -110 -90 -70 -50 -30 -100 20 40 60 80 100 120 140 160 180

Dihedral Angle

Energy (kJ/mol)

Energy

p-p Overlap Required for -Bond

OverlapOverlap No OverlapNo Overlap

pZ pZ pZ

No LongerpZ Orbital

H2C=CH2 Structure

• The C=C double bond is shorter (1.33 Å) than a single C—C bond (1.54 Å)

• C=C is much stronger (611 kJ/mol) than a single C—C bond (376 kJ/mol)

Acetylene HCCH

• Two sp hybrid orbitals from each carbon overlap to form one sp–sp -bond

• In addition, the pz orbitals from each carbon form a pz–pz bond by sideways overlap and py orbitals overlap similarly

+ + Bonding in Acetylene

• Sharing of 6 valence e— forms a triple bond ( + 2)• The two sp orbitals at the ends form -bonds with

the terminal hydrogens

Acetylene Structure• The triple bond length in acetylene (1.20 Å) is far

shorter than ethane (1.54 Å) or ethylene (1.33 Å)• The triple bond is far stronger (835 kJ/mol)

Hybridization of Nitrogen• In ammonia, NH3, the nitrogen atom has 5 outer-shell e— and it forms 3

covalent bonds with 3 hydrogen atoms to fill its valence e— octet

• H–N–H bond angle in NH3 is 107.3°, close to the tetrahedral angle observed in methane CH4

• One sp3 orbital is occupied by a lone pair of e—, and 3 sp3 orbitals have one electron each, forming bonds to the 3 H atoms

• NH3, the N–H bond length is 100.8 pm, and bond strength is 449 kJ/mol

The Nitrogen Lone Pair is Basic• Nitrogen-containing compounds derived from :NH3 are the most

common organic bases• The lone pair on :NH3 can form a bond with H+ to form an ammonium

ion +NH4 • We can refer to this process as protonation of a lone pair, and such a

lone pair is referred to as a protonated lone pair

NH

HH

Ammonia

lone pair

H NH

HH

H

Ammonium Ion

sp2 and sp Hybridized Nitrogen

• Carbon-nitrogen double bonds (C=N) are called imines

• Sections 19.10 and 19.11 (pp 696—702) cover the some important reactions that produce and use imines

• Carbon-nitrogen triple bonds are called nitriles (cyanides)

• These important compounds are generally regarded as derivatives of carboxylic acids (Chapter 20)

Hybridization of Oxygen• The oxygen atom in H2O is sp3-hybridized• Oxygen has 6 valence-shell e— but forms only 2 bonds, leaving two

lone pairs• The H–O–H bond angle in water is 104.5°— This is less than the

tetrahedral angle due to e— e— repulsion between the two lone pairs• The O–H bond length is 95.8 pm, and the bond strength is 498 kJ/mol

The e— e— repulsion pushesthe two H’s closer together

sp2 and sp Hybridized Oxygen

• Carbon-oxygen double bonds (C=O) are called carbonyls

• Carbonyls are present in aldehydes, ketones, carboxylic acids, carboxylic esters, and amides (peptide bonds)

• Understanding the carbonyl and its reactivity are among the most important concepts in Organic Chemistry

• sp hybridized oxygen is extremely rare in Organic Chemistry

• The only important example is carbon monoxide CO

Protonation of Oxygen

• Oxygen lone pairs are not as basic as nitrogen lone pairs, but can be protonated by strong acids

• Protonation of oxygen provides intermediates that are very important for catalysis

O

HOOH

OH

H+

ProtonatedCarbonyl

O O

H2O

H—