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Transcript of McMurry Chapter 1 Structure & Bonding Organic Chemistry I S. Imbriglio.
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McMurry Chapter 1
Structure & Bonding
Organic Chemistry IS. Imbriglio
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Organic Chemistry: What is it?
• 1770: Organic chemistry referred to compounds isolated from living things.
__________ belief that a “magic” force, present in plants and animals, is required to make organic compounds
• 1789: Lavoisier observed that organic compounds are composed primarily of __________________________
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Organic Chemistry: What is it?• 1816: Michel Chevreul showed that one organic
compound could be converted into others.
• 1828: Friedrich Wohler converted an inorganic compound into an organic compound.
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Organic Chemistry: the study of carbon compounds
• ________of all known compounds are composed of carbon (~30 million known compounds)
• ________of chemists define themselves as organic
• Organic chemistry is crucial to our way of life: Pharmaceutical, Petroleum, Materials/Polymer, OUR BODIES!
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Why Carbon?What makes carbon so special? (3 things)
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Why Carbon?• Carbon atoms form __________________ bonds
to other atoms (including other carbon atoms).
Incredible Structural Diversity!
O
OH
H
OH
H
H
OHOHH
H
OH
OH
HH
H OH
OH HO
HOHO
H
N
N NH
N
NH2
NH
NH
O
O
H2N CH C
CH3
OH
OH2N CH C
CH2
OH
O
HO
H H
H
CH3OH
CH3 H
CH3OH
H H
O
Carbohydrates Amino Acids
DNA Bases Hormones
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Review of the AtomAtomic Structure:
– ___________ charged nucleus – dense and small – _______________ charged electrons in a cloud
around the nucleus– Diameter approximately 2 10-10 m
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Review of the AtomOrbitals:- Three-dimensional shapes indicating where the
electron is most likely to be found – s, p, d, f- We will focus on s and p orbitals – carbon atoms do
not have d or f orbitals
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Review of the AtomOrbitals:- Orbitals are organized into different shells and
subshells- In the ground state of an atom, electrons occupy
the lowest energy orbitals
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Review of the AtomElectron Configurations:
– _________ electrons per orbital (max)– When two electrons occupy the same orbital, they
must have opposite spins (Pauli Exclusion Principle)– If two or more empty orbitals of equal energy are
available, electrons occupy each with spins parallel until all orbitals have one electron (Hund’s Rule)
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• Write the electron configuration for oxygen.O
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Review of Chemical Bonding• Atoms bond together
because the compound that results is more _________ than the separate atoms – bond formation is always exothermic.
• The Octet Rule: In most cases, atoms will _______ __________________ electrons to gain an octet.
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Review of Chemical Bonding• An _____________ is the electrostatic attraction
between a cation (____) and an anion (____).• The two bonded atoms do not share electrons.
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Review of Chemical Bonding• ___________________ occurs between atoms of similar
electronegativity – very important in organic chemistry.
eg. CCl4 is covalent . . . Why?
Large thermodynamic penalty for ionizationof carbon to C4+.
C
1s22s22px12py
1
C4+
1s2 = [He]
4e– H = +1480.7 kcal/mol(ionization potential)
+
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Review of Chemical Bonding
• Instead of transferring electrons, each chlorine atom shares one valence electron with carbon so that every atom has a filled valence shell (an octet).
Lone Pairs: ____________________________________________
C 4 ClCCl
Cl
Cl
Cl
Lone Pairs
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Review of Chemical Bonding• Covalently bonded compounds are represented by
Lewis or Kekulé structures.• Lone pairs will be included in this class.
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Review of Chemical Bonding• The number of covalent bonds that a main group
element must form to achieve an octet equals eight minus its group number.
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Keeping the common bonding patterns in mind, draw a valid Kekulé structure for each of the following formulas. Include all lone pairs.
CH3NH2 H2O2 C3H8
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Review of Chemical BondingMultiple Covalent Bonds• Atoms can share more than one electron pair to gain
a full octet.– _________________: two electron pairs shared
between two atoms– _________________: three electron pairs shared
between two atoms
C CH
H H
H
ethylene acetylene
C C HH
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Review of Chemical Bonding
C C C N N N O O F
Summary of Bonding (Neutral Atoms - Row 2)
C
Group 4A Group 5A Group 6A Group 7A
• Atoms will form combinations of single, double and triple bonds to gain a full octet.
4 total bonds 3 total bonds 2 total bonds 1 bond
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Draw a valid Kekulé structure for each of the following formulas. Include all lone pairs.
CH3CO2H HCN
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Review of Chemical BondingValence Bond Theory• Covalent bond forms when two atoms approach each
other closely so that a singly occupied orbital on one atom overlaps a singly occupied orbital on the other atom
• Electrons are paired in the overlapping orbitals and are attracted to nuclei of both atoms
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• Carbon uses its four valence electrons to form four covalent bonds.
• Methane is a perfect tetrahedron – all of the C-H bonds are equivalent.
• The four orbitals that make those bonds must also be equivalent.
Review of Chemical Bonding
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Review of Chemical BondingHybridization• Atomic orbitals (s, p) on the same atom can be
combined to form hybrid orbitals (sp, sp2, sp3) with geometries similar to those observed experimentally.
• Hybrid Orbitals:– Are more directional (better bonding overlap
with orbitals on other atoms)– Minimize electron-electron repulsion (think
VSEPR)
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Review of Chemical Bonding
• sp3 Hybridization: One s and three p orbitals combine to form four new sp3 hybrid orbitals.
The large lobes of the four sp3 orbitals are pointed 109.5 from each other – a tetrahedral geometry.
largelobe
backlobe
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Review of Chemical Bondingsp3 Hybridization in Methane• Each sp3 orbital on carbon overlaps with a 1s orbital
on hydrogen to form four sigma bonds.• ___________________: cylindrically symmetrical bond
resulting from head-on overlap of two orbitals along the bonding axis
C
H
H HH
Orbital Picture Ball & Stick Model Space-Filling Model
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Review of Chemical Bondingsp3 Hybridization in Ethane• The two carbon atoms are bonded together by sigma
overlap between the two sp3 orbitals.• Three sp3 orbitals on each carbon are used to form C-H
sigma bonds.
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Review of Chemical Bonding• sp2 Hybridization: One s orbital combines with two p
orbitals to give three new sp2 hybrid orbitals
• One p orbital is left unhybridized.
• The large lobes of the sp2 orbitals are pointed 120 from each other – a trigonal planar geometry.
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Review of Chemical Bondingsp2 Hybridization in Ethylene• Two sp2 orbitals overlap head-on to form a sigma bond
– Electrons in the sigma bond are along the bonding axis• Two p orbitals overlap side-by-side to form a pi bond
– Electrons in the pi bond occupy regions above and below the bonding axis (not cylindrically symmetrical)
C CH
H H
H
ethylene
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Review of Chemical Bonding• sp Hybridization: One s and one p orbital combine to
form two new sp hybrid orbitals
• Two p orbitals left unhybridized
• The large lobes of the sp orbitals are pointed 180 from each other – a linear geometry
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Review of Chemical Bondingsp Hybridization in Acetylene• Two sp orbitals overlap head-on to form a sigma bond• Two vertical p orbitals overlap side-by-side to form pi
bond• Two horizontal p orbitals overlap side-by-side to form
pi bond
acetylene
C C HH
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Review of Chemical Bonding
Assigning Hybridization to Atoms• The hybridization of an atom in a molecule can
be determined by counting the number of hybrid orbitals the atom is using.
• Hybrid orbitals are used to:– Form sigma bonds (not pi bonds)– Hold lone pairs
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Review of Chemical BondingAssigning Hybridization to Atoms• The number of hybrid orbitals on an atom must be
equal to the number of atomic orbitals that were “mixed together” to form the hybrid orbitals.
eg. One s orbital plus three p orbitals gives four sp3 orbitals
# hybrid orbitals hybridization geometry
4 sp3 tetrahedral
3 sp2 trigonal planar
2 sp linear
approx. bond angles
109°
120°
180°
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Review of Chemical BondingAssigning Hybridization to Atoms• Heteroatoms also use hybrid orbitals to form
sigma bonds and hold lone pairs.• Below are examples of sp3-hybridized nitrogen
and oxygen.
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Determine the hybridization of each non-hydrogen atom in the following molecules.
C C C CH
HH
O
CH3
C C NHH
H
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Representing Molecules
Condensed Structures
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Representing Molecules
• Lewis and Kekulé structures are only adequate for very small molecules.
C
CC
C
CC
CC
CC C
CC
C
CC
C
O
CH3 H
CH3OH
H
HH
H H HH
H HH
HH
HH
HH H
HH
H
Testosterone(not so easy)
CC
C
H H
Propane(pretty easy)
H
HH
H
HH
O
O
O
OO
O
O
O
OO
OH
H3C
H HH
HH
HO H2C H
O
H
CH3 CH3 CH3
HH
HH
H H
HH
H
Brevetoxin A (!!)
Just imagine...
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Representing MoleculesSkeletal Structures (Line-Angle Formulas)
Rules for Drawing Skeletal Structures1. Do not draw carbon atoms. A carbon atom is
assumed to be at each intersection and at the end of each line.
2. Do not draw hydrogen atoms bonded to carbon. Assume enough C-H bonds to give each carbon a filled valence.
3. Draw all heteroatoms and attached hydrogens.
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Representing Molecules
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Convert the following Kekulé structures to skeletal structures. Show all lone pairs.
CC
OH
H H
H
HH
Ethanol
C
C C
CH H
HH
H
H H
H
Cyclobutane
CC
CCC
C CC
O
OH
H CH
HH
HH
CH
H
Ibuprofen
CC
C
HH
HH HH
H
HH
CC
O
C
H
H
HH
H
H
Acetone
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Representing Molecules
• Dashes and Wedges: Molecules are not flat.
H
CH H
HCH4
109.5°H
H HH
lines
wedge
dashmethane
lines: in the plane of the paperdashes: going back into the paper (away from you)wedges: coming out of the paper (toward you)