What you should remember from the last lecture •  The syllabus is at h"p://www.chem.uky.edu/courses/che230/ •  Lewis Dot Structures and Formal Charges. Be able to construct these for any main group atoms/molecules, for single and mul:ple bonds. •  Isomers. Same molecular formulae, different structures. Be able to construct many. •  Resonance – different ways to distribute electrons within a structure. The hybrid is the only thing that is real. What you should remember from the last lecture 1.  Electron configura:ons for the elements 2.  The Octet Rule 3.  Lewis Dot Structures 4.  Calcula:on of Formal Charges (and the actual distribu:on of charges due to electronega:vi:es) H
O
H
H
H
H
H
O
H
8 electrons on oxygen H
C
H
H
H
C
6 electrons on carbon H
Today Hybridiza:on Sigma and π bonding, bond lengths and strengths For Prac:ce: Construct the Lewis Dot Structure, assign formal charges, and predict bond polari:es for the following: H
C O
Carbon monoxide H C N C
H
Methyl isocyanide Alkynes you may know….. OH
Ethinylestradiol H
O
H
H
HO
CH3S
S
H
N
OCH3
S
HO
O
O
H
I
O
S
O
OCH3
O
HO
OCH3
O
O
NH
HO
O
OH
H
N
O
CH3O
CH3O
OH
Calicheamicin Today Hybridiza:on Sigma and π bonding, bond lengths and strengths For Prac:ce: Construct the Lewis Dot Structure, assign formal charges, and predict bond polari:es for the following: H
C O
Carbon monoxide H C N C
H
Methyl isocyanide What you should remember from the last lecture •  HybridizaFon – The mixing of atomic orbitals to form hybrid orbitals. •  The # orbitals in = # orbitals out. •  sp3, sp2, and sp hybridizaFons – know what they look like, the number of hybrid orbitals and the number of p orbitals. •  Geometry: sp3 orbitals are 109.5˚ apart (tetra-­‐hedral), sp2 orbitals are 120˚ apart (trigonal), and sp orbitals are 180˚ apart (linear). •  Resonance. Different alloca:ons of electrons within Lewis structure. Individual resonance forms do not exist. The “hybrid” is the only thing that is real. Today Hybridiza:on Sigma and π bonding, bond lengths and strengths For Prac:ce: Construct the Lewis Dot Structure, assign formal charges, and predict bond polari:es for the following: H
C O
Carbon monoxide H C N C
H
Methyl isocyanide Which Lewis Dot Structure is “Right”? C
C
O
C
δ
δ
O
C
C
O
O
O
C O
5 electrons around C 7 electrons around O C O
6 electrons around C 8 electrons around O C O
8 electrons around C 8 electrons around O C O
The ‘hybrid’ Dipole moment is 0.12 D (very small). Which Lewis Dot Structure is “Right”? H
H
C
C
N
H
H
H
H C N
H
H
δ
C
H
The ‘hybrid’ H
H C N
H
H C N C
H
δ
H C N C
7 electrons around N 5 electrons around C H
H C N C
H
8 electrons around N 6 electrons around C H
C
H C N C
H
8 electrons around N 8 electrons around C A Lifle Hybridiza:on Prac:ce sp2 (one π bond, therefore one p orbital) 2
O
NH
N
HO
H
O
H
1
H
N
N
O
sp3 (no π bonds, therefore no p orbitals) H
N
H
3
4
sp2 (one π bond, therefore one p orbital) sp (two π bonds, therefore two p orbitals) Azidothymidine (Zidovudine, AZT) A Lifle Hybridiza:on Prac:ce OCH3
H
N
O
OCH3
H
S
N
O
CO2H
sp2 (one π bond, therefore one p orbital) Penicillin G What you should remember from the last lecture •  sp3, sp2, and sp hybridizaFons – Be able to iden:fy the hybridiza:on of carbon and of heteroatoms (oxygen, nitrogen, etc). Be able to determine what orbitals contains non-­‐bonding pairs of electrons on N and O. •  Acid-­‐Base Chemistry. Remember the defini:ons of Lewis and Bronsted acids, Ka and pKa and how to use these numbers to predict Keq for acid-­‐base reac:ons. Make a predic:on! Longer (~1.54 Å) formed by overlap of two sp3 orbitals Glutathione (a supremely important anFoxidant) SH
O
O
1
O
H
N
N
H
HO
NH2
OH
O
2
Shorter (~1.5 Å) formed by overlap of an sp3 orbital with an sp2 orbital H
N
Methamphetamine 3
4
EssenFally idenFcal! (~ 1.4 Å) H
N
Drugs du Jour OH
HO
H
N
H
N
HO
CH3
CH3
CH3
HO
Ephedrin Adrenaline OH
H
N
CH3
CH3
Pseudoephedrin O
H
N
CH3
CH3
Methamphetamine H
N
O
CH3
CH3
Methenedioxy methamphetamine (MDMA, ecstasy) What you should remember from the last lecture •  sp3, sp2, and sp hybridizaFons – Be able to iden:fy the hybridiza:on of carbon and of heteroatoms (oxygen, nitrogen, etc). Be able to determine what orbitals contains non-­‐bonding pairs of electrons on N and O. •  Acid-­‐Base Chemistry. Remember the defini:ons of Lewis and Bronsted acids, Ka and pKa and how to use these numbers to predict Keq for acid-­‐base reac:ons. What you should remember from the last lecture •  Acid-­‐Base Chemistry. Remember the defini:ons of Lewis and Bronsted acids, Ka and pKa and how to use these numbers to predict Keq for acid-­‐base reac:ons. Remember some pKa’s: •  RS-­‐H •  RO-­‐H •  RNH-­‐H
•  RCH2-­‐H
R C
C
10 16 35 45-­‐50 H
24 R
O
42 CH2
20 CH2
H
H
O
4.7 O
H
One note on acid-­‐base equilibria H3PO4 + H2O
pKa 2.2
NH2
H2PO4 + H3O
pKa -1.7
N
N
N
HO
N
NH2
N
O
H
O
H
H
O
H
P
H
N
O
O
O
H
O
H
H
O
H
P
O
O
H
N
N
What you should remember from the last lecture •  Acid-­‐Base Chemistry. Remember the defini:ons of Lewis and Bronsted acids, Ka and pKa and how to use these numbers to predict Keq for acid-­‐base reac:ons. Remember some pKa’s: •  RS-­‐H •  RO-­‐H •  RNH-­‐H
•  RCH2-­‐H
R C
C
10 16 35 45-­‐50 H
24 R
O
42 CH2
20 CH2
H
H
O
4.7 O
H
What you should remember from the last lecture FuncFonal Groups. A commonly occurring group of atoms with characterisFc chemistry and properFes. Drawing. Be aware of condensed drawing conven:ons: CH3CH2CH2CH3 and Alkanes: Hydrocarbons with no mul:ple bonds. Alkenes: Hydrocarbons with one or more C-­‐C double bonds. Alkynes: Hydrocarbons with one or more C-­‐C triple bonds. AromaFc Hydrocarbons: Hydrocarbons related to benzene and other cyclic polyenes. Some aroma:cs of interest O
OH
Benzo[a]pyrene OH
Benzo[a]pyrene-­‐ 7,8-­‐dihydrodiol-­‐9,10-­‐epoxide Exam 1 in class next Wednesday 1. 
2. 
3. 
4. 
Get a good night’s sleep beforehand. Eat a decent breakfast. Bring photo ID. The exam will cover everything we have covered in class through next Monday. Before you begin this exam: First: You are allowed to have a simple model set at your seat. Please put away all other materials. Calculators will not be needed. Second: Place your student iden:fica:on on your desk. A proctor will come around to check everyone’s ID. Third: Read through the en:re exam. Your goal is to score as many points as possible. Do not waste :me on problems that you can’t do if there are others that look easy. Fourth: READ EACH QUESTION CAREFULLY. Be sure you answer the ques:on that is asked. FiOh: This exam must be turned in by 8:50 AM SHARP. There will be no extensions, so budget your :me carefully. A bit of prac:ce….. Which is the shortest bond: of this pair: 1.11 Å 1.09 Å 1
2
H
H
CH2
Which is the strongest bond: of this pair: 2
1
98 kcal/mol 125 kcal/mole H
H
CH2
Which is the most acidic bond: of this pair: pKa 45 2
1
pKa 24 H
CH2
H
What you should remember from the last lecture FuncFonal Groups. A commonly occurring group of atoms with characterisFc chemistry and properFes. Drawing. Be aware of condensed drawing conven:ons: CH3CH2CH2CH3 and Alkanes: Hydrocarbons with no mul:ple bonds. Alkenes: Hydrocarbons with one or more C-­‐C double bonds. Alkynes: Hydrocarbons with one or more C-­‐C triple bonds. AromaFc Hydrocarbons: Hydrocarbons related to benzene and other cyclic polyenes. What you should remember from the last lecture FuncFonal Groups. A commonly occurring group of atoms with characterisFc chemistry and properFes. Alcohols, amines, and thiols. These related func:onal groups (-­‐OH, -­‐SH, -­‐NH2) have func:onal groups with lone pairs of electrons. These are nucleophiles: tend to react with electron-­‐deficient sites in other molecules. Alkyl halides: Compounds with a C-­‐X bond (X=halogen). The electronega:vity of halides makes the carbon somewhat electron-­‐
deficient. These are electrophiles. A bit of prac:ce….. Which acid-­‐base reac:on is favorable (i.e. Keq >1)? OH
O
CH3 Li +
CH4
pKa = 16
RS-­‐H RO-­‐H
RNH-­‐H
RCH2-­‐H
10 16 35 45-­‐50 R
+
O
pKa = 45
C
H
C
R
20 24 O
42 CH2
O
P
O
O
CH3
CH3
P
CH3
P
CH3
CH3
CH2
O
H
What are the formal charges on O and P? CH3
Li
4.7 H
H
What you should remember from the last lecture Carbonyl-­‐based Func:onal Groups: O
O
H
Ester Aldehyde OR
O
O
Amide Ketone NR2
O
O
Acid Chloride Carboxylic Acid Cl
OH
C
N
Nitrile Hydrogen bonding in pep:des O
R
H
N
N
H
O
O
O
H
H
R
O
R
O
O
H
O
R
O
N
O
O
O
O
H
R
O
N
O
N
H
H
O
H
N
H
N
R
H
R
N
R
N
R
O
R
N
H
H
N
H
N
H
N
R
H
R
N
R
N
N
O
O
R
H
N
N
R
H
O
A bit of prac:ce….. Which acid-­‐base reac:on is favorable (i.e. Keq >1)? OH
O
CH3 Li +
CH4
pKa = 16
RS-­‐H RO-­‐H
RNH-­‐H
RCH2-­‐H
10 16 35 45-­‐50 R
+
O
pKa = 45
C
H
C
R
20 24 O
42 CH2
O
P
O
O
CH3
CH3
P
CH3
P
CH3
CH3
CH2
O
H
What are the formal charges on O and P? CH3
Li
4.7 H
H