Organic Chemistry - 246A Homework DUE Friday, 5 Sept Problems in McMurry 1.24; 1.28; 1.31; 1.45; 1.46; 1.47 => (1.48—1.52 BONUS Problems)

Hybridization of C, N & O sp3, 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 (s) 2 bonding e— sp2 Orbitals make double bonds (s + p) 4 bonding e— sp Orbitals make triple bonds (s + p + p) 6 bonding e—

Ethylene H2C=CH2 sp2 orbitals are in a plane with120° angles 90 120 sp2 orbitals are in a plane with120° angles The remaining p orbital is 90° perpendicular to the plane containing the sp2 orbitals Two sp2 orbitals interact to form a double bond, one s-bond + one p-bond

Dihedral Rotation of Ethane

Dihedral Rotation of Ethylene

p-p Overlap Required for p-Bond No Overlap pZ pZ No Longer pZ 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 s-bond In addition, the pz orbitals from each carbon form a pz–pz  bond by sideways overlap and py orbitals overlap similarly

s + p + p Bonding in Acetylene Sharing of 6 valence e— forms a triple bond (s + 2p) The two sp orbitals at the ends form s-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

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 pushes the 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