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Organic Chemistry John McMurry 6th Ed교재 및 참고문헌
중간고사(2회): 100점 기말고사(1회): 100점연습문제 및 출석및 수업참여도: 50점
1.008 for hydrogen: 1H (99.985%, 1.0078), 2H (0.015%, 2.0141)12.011 for carbon: 12C (98.89%, 12.000), 13C (1.11%, 13.0034)
Ch.1 Structure and Bonding
Isotope: same atomic number but different mass number (different number of neutrons)
All the atoms in a given element have the same atomic number but they can have different mass numbers depending on how many neutrons they have.
Atomic weight: the weighted average atomic mass units of an element’s isotopes
- electron distribution: quantum mechanics- wave equation solution: wave function (ψ) or orbital: wave function of one electron atom
s orbital p orbital d orbitals
1.2 Atomic Structure: Orbitals
Ch.1 Structure and Bonding
shapes of orbitals: s, p, d, f
ψ2 ; the volume of space around a nucleus where an electron can most likely be found (probability)
shells: atomic orbitals with the same principal quantum number
1s
2s
2p
3s
3p
3d
ener
gy
1st shell
2nd shell
3rd shell(18 e-)
(8e-)
(2 e-)
Ch.1 Structure and Bonding
- distribution of electrons in an atom: each orbital can occupy 2 e-
shapes of 2 p orbitals
2px orbital
x
y
z
2py orbital
x
y
z
2pz orbital
x
y
z
Ch.1 Structure and Bonding
node: a region of zero electron densitynodal plane:
1.3 Atomic Structure: Electron Configuration
Ch.1 Structure and Bonding
ground-state electron configuration: lowest-energy arrangement
rule 1: The lowest-energy orbitals fill up first (Aufbau principle)
1s 2s 2p 3s 3p 4s 3d
1s
2s
2p
Energy
Ch.1 Structure and Bonding
rule 2: Only two electrons can occupy an orbital and they must be of opposite spin (Pauli exclusion principle): electrons spins (↑) or (↓)
1s
2s
2p
Ch.1 Structure and Bonding
If two or more orbitals of equal energy are available, one electron occupies each until all orbitals are half-full. Only then does a second electron occupy one of the orbitals (Hunt’s rule): The electrons in the half-filled orbitals all have the same spin
rule 3:
1s
2s
2p
1sHydrogen
1atomic number
1s
2s
2pCarbon
6atomic number
Ch.1 Structure and Bonding
ground-state electron configurations of some elements
1s
2s
2pOxygen
8atomic number
Ch.1 Structure and Bonding
ground-state electron configuration of oxygen
Ch.1 Structure and Bonding
Practice
Chloride: atomic number 17
1s
2s
2p
3s
3p
1.4 Development of Chemical Bonding Theory
In 1858, Kekule-Couper: tetravalent carbon
In 1865, Kekule-Couper: multiple bonding, ring systems
In 1874, van't Hoff: tetrahedral carbon (3-dimensional)
(2-dimensional)
Cin plane
dashed line (behind the plane)
heavy wedged line (out of the plane)
Ch.1 Structure and Bonding
1.5 Covalent Bonds
Why do atoms bond together?
Ch.1 Structure and Bonding
How can bonds be described electronically?difficult to answer
Because the compound is more stable, has less energy than the separate atoms
Octet rule: 8 electrons in valence shell, special stability; noble-gas configuration
Ne (2 + 8); Ar (2 + 8 + 8); Kr (2 + 8 + 8 + 8)
Na Na+ + e-
1s2 2s2 2p6 3s1 1s2 2s2 2p6
Ch.1 Structure and Bonding
group 1A (alkali metal): loose 1 electron
group 7A (halogen): gain 1 electron
Cl Cl-+ e-
1s2 2s2 2p5 1s2 2s2 2p6
Ch.1 Structure and Bonding
Cl-Na+
ionic bond: held together by electrostatic attraction
C C4+ + 4 e-
1s2 2s2 2p2 1s2X
How about the middle elements?
- satisfy octet by sharing electrons: covalent bond
Ch.1 Structure and Bonding
1s1 2s2 2p2
H C
2s2 2p3
N
2s2 2p4
O
2s2 2p5
F
molecule: the neutral collection of atoms held together by covalent bonds
Lewis structure or electron-dot structure:
- valence electrons are represented by dots
Ch.1 Structure and Bonding
C
H
H H
H
OH
H
N
H
H H FH
CH4 H2O NH3 HF
C
H
H
H
O
H
CH3OH
Ch.1 Structure and Bonding
H Cl
Br FO
N
B
C
one bond two bond
three bond four bond
Ch.1 Structure and Bonding
nonbonding electrons (lone-pair electrons); valence electrons that are not used for bonding
N
H
H HNH3 H N HH
Kekule structure (line-bond structure)
Ch.1 Structure and Bonding
CH4 H2O NH3 CH3OH
CH
H HH
OH H NH
H H CH
H OH
H
C
H
H H
H
OH
H
N
H
H H FH
CH4 H2O NH3 HF
Lewis structure
Kekule' structure
Ch.1 Structure and Bonding
PH?
Practice
GeCl?
AlCl? CH?Cl?
PH3PH
HH
P : 5A
GeCl4GeCl
ClCl
Cl
Ge : 4A
AlCl3AlCl
ClCl
Al : 3A
CH2Cl2CH
HCl
Cl
C : 4A
1.6 Valence Bond Theory and Molecular Orbital Theory
How does the electron sharing occur?
Ch.1 Structure and Bonding
two models for covalent bond formation
valence bond theory
"electrons are localized around the bond"
molecular orbital theory
"electrons are delocalized over the molecule"
explains wellσ-bonds
explains wellπ-bonds
Ch.1 Structure and Bonding
Valence Bond Theory
key ideas
• Covalent bonds are formed by overlap of two atomic orbitals, each of which contains one electron. The spins of the two electrons are opposite.
• Each of the bonded atoms retains its own atomic orbitals, but the electron pair in the overlapping orbitals is shared by both atoms.
• The greater the amount of orbital overlap, the stronger the bond.
H H+ H H
1s H2 molecule1s
Ch.1 Structure and Bonding
H H
circular cross-section
- H-H bond is cylindrically symmetrical
sigma (σ) bond: bonds formed by the head-on overlap of two orbitalsalong a line drawn between the nuclei
too close: nuclei repeltoo far: unable to share electrons→ optimum distance for maximum stability: bond length
Ch.1 Structure and Bonding
ener
gy
H2 molecule
two hydrogen atoms
436 kJ/mol (104 kcal/mol)
2 H H2
released when bond formedabsorbed when bond breaks
How close are the two nuclei in the H2 molecule?
Ch.1 Structure and Bonding
ener
gy 0
+
_
HH (too close)
H H
H H (too far)
74 pmbond length
A plot of energy versus internuclear distance for two hydrogen atoms.
Ch.1 Structure and Bonding
1.12 Molecular Orbital Theory
key ideas
• Molecular orbitals describe regions of space in a molecule where electrons are most likely to be found, and they have a specific size, shape, and energy level.
• Molecular orbitals are formed by combining atomic orbitals. The number of MO's formed is the same as the number of atomic orbitalscombined.
• bonding MO: lower in energy than the starting atomic orbitalsantibonding MO: higher in energynonbonding MO: same energy
Ch.1 Structure and Bonding
ener
gy
H 1s orbital H 1s orbital
H H antibonding MO (unfilled)
H H bonding MO (filled)
H H
H H
1.7 Hybridization: sp3 Orbitals and the Structure of Methane
Hydrogen molecule is simple, but complicate for tetravalent carbon atom
Ch.1 Structure and Bonding
Carbon uses two kinds of orbitals (2s22p2) to form bondsbut four identical bonds (tetrahedral). How?
Hybridization (1931, Linus Pauling): mathematically explained how an s orbital and three p orbitals can combine (sp3 orbitals)
- valence bond theory
2s 2py
2pz2px
hybridization
4 identical tetrahedral sp3 orbitals
an sp3 orbital
Ch.1 Structure and Bonding
Hybridization
Ch.1 Structure and Bonding
• hybridized sp3 orbitals are unsymmetrical: one of two lobes is much larger, and form stronger bonds than unhybridized s or p orbitals
• unsymmetrical sp3 orbitals: two lobes of p-orbital have opposite signs
2s 2px
hybridization
an sp3 orbital
+_+ +_
Ch.1 Structure and Bonding
H
CH H
H
109.5 o 110 pmbond angle(tetrahedral)
bond length
• C-H bond strength in methane: 438 kJ/mol (105 kcal/mol)
1.8 The Structure of Ethane• σ-overlap of two sp3 orbitals
Ch.1 Structure and Bonding
C
H
HH
109.6 o
154 pm
C C
H
H
H
H
H
HCH3CH3
CC CC
C
H
HH
• C-H bond strength in ethane: 420 kJ/mol (100 kcal/mol)C-C bond strength in ethane: 376 kJ/mol (90 kcal/mol)
1.9 Hybridization: sp2 Orbitals and the Structure of Ethylene
• C2H4; double bond, planar
Ch.1 Structure and Bonding
CH
H
121.7 o
133 pm
CH
H
C CH
H
H
HC C
H H
HH
116.6 o107.6 pm
Ch.1 Structure and Bonding
s + 2 (p) → 3 (sp2)
3 identical sp2 orbitals
p
π-bond
σ-bond
• C-H bond strength in ethylene: 444 kJ/mol (106 kcal/mol)C=C bond strength in ethylene: 611 kJ/mol (146 kcal/mol)
Ch.1 Structure and Bonding
Molecular orbital description C=C π-bond
Ch.1 Structure and Bonding
combine
nodal plane
π-antibonding (π*) MO
π-bonding (π*) MO
Actually, p-orbitals have two lobes with opposite signs.
C OH
HC O
H
H
Lewis structure Line-bond structure
Ch.1 Structure and Bonding
Practice
Line-bond structure, hybridization of carbon?
CH2O
sp2
C CC
H
HH
HH
H
Ch.1 Structure and Bonding
Practice
Line-bond structure, hybridization of carbon?
CH3CH=CH2
sp3
sp2
1.10 Hybridization: sp Orbitals and the Structure of Acetylene
• C2H2; triple bond, linear
Ch.1 Structure and Bonding
180 o
C CH HC CH H
106 pm120 pm
Ch.1 Structure and Bonding
s + 1 (p) → 2 (sp)
2 identical sp orbitals
pp
π-bond
σ-bondπ-bond
• C-H bond strength in acetylene: 552 kJ/mol (132 kcal/mol)C≡C bond strength in acetylene: 835 kJ/mol (200 kcal/mol)
Ch.1 Structure and Bonding
Ch.1 Structure and Bonding
107.6106444C(sp2)-H
106132552C(sp)-H
110100420C(sp3)-H
120200835C(sp)≡C(sp)HC≡CH
133146611C(sp2)=C(sp2)H2C=CH2
15490376C(sp3)-C(sp3)CH3CH3
Bond Length(pm)kcal/molkJ/mol
BondMoleculeBond Strength
110105438C(sp3)-HCH4
Comparison of C/C and C/H bonds
Ch.1 Structure and Bonding
Summary of Hybridizations
tetrahedral: sp3 hybrid
planar: sp2 hybrid
linear: sp hybrid C CH3C CH3
CH4 CH3-CH2-CH2-CH3
C CH3C CH3
H H
C CCH
HH
H
Ch.1 Structure and Bonding
Practice
Line-bond structure, hybridization of carbon?
CH3C≡CH
sp3
sp
C C C
H
H
H
H
Ch.1 Structure and Bonding
Practice Hybrid, Geometry?
CH2=C=CH2
C C C
H
H H
H
C CCH
H H
H
sp2 sp2
sp
C C C
H
H H
H
C C C
H
H H
H
1.11 Hybridization of Other Atoms: Nitrogen and Oxygen
• covalent bonds of other elements can also be described by hybridization
Ch.1 Structure and Bonding
NH3 NH
H H
NH H
H
107.3 o
100.8 pm bond lengthN-H: 449 kJ/mol (107 kcal/mol)
sp3
Ch.1 Structure and Bonding
H2O OH H
O
HH
104.5 o
95.8 pm bond length
O-H: 498 kJ/mol (119 kcal/mol)
sp3
C NHH
H
Ch.1 Structure and Bonding
Practice
Line-bond structure, hybridizations?
Formaldimine, CH2NH
C NHH
H
sp2
sp2
OCH3
H
Ch.1 Structure and Bonding
Practice Geometry?
CH3OHCH3NH3CCH3
CH3
N
CH3
CH3 PH
HH
PH3
1.12 Hybridization of Carbon Species
Carbocation
Ch.1 Structure and Bonding
C C sp2
planar
CC
sp3
Carbanion
Chemical Toxicity and RiskChemistry @ Work
All chemicals are toxic to some extent, and the difference between help and harm is matter of degree.
LD50 value: the amount of a substance per kilogram body weight that is lethal to 50% of the test animals. The lower the value, the more toxic the substance.