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Organic Chemistry(Smith) 1.Structure and Bonding\ (2.Bonding (through…
Organic Chemistry(Smith)
1.Structure and Bonding\
1.The Periodic Table
same raw - similar size
same coumn - similiar electronic and chemical properties
p has dumbbell shpe
N-13 is used for PET
8.Drawing Organic Structure
Condensed structures
sceletal str
11.Bond Length and Bond Strength
As the number of electrons between two nuclei increases, bonds become shorter and stronger(triple shorter and stronher than double, which is stronger and shorter than single)
C-H bond
percent of s-character
indicates the fraction of a hybrid orbital due to the 2sorbital
increased percent s-character-->increased bond strength-->Decreased bond length
4.Isomers
Constitutional isomers - connectivity of atoms deffer
Polarity of Molecules
net dipole
sum of all dipole moments
to determine whether molecule has a net dipole
identify all of the polar bonds and the directions of bond dipoles
ditermine the geometry around individual atoms and decide whether indiv. dipoles cancel or reinforce each other in space
H2O is polar (bend molecuke, geometry reinforce net dipole), CO2 is unpolar (linear molecule, geometry cancel net dipole)
6.Resonance
resonance structures have different arrangment of electorns and same Lewis strructures
structure is resonance hybrid and represents properties of both res. str
"better" res. str - major contributor (has more bonds and fewer charges), all other - minor contributor
hybrid contains marks of the postion of a multiple bond (=) and site of charge. Double bond in differ. res structure marks dashed and solid line; location of charge by partial charge (δ+,δ-)
res. st. are not real
are not in equilibrium with each other
3.not isomers.
9.Hybridization
σ
all single bonds
the lowest energy arrangement of electrons - ground state (opposite is excited state)
sp3 hybrids form from one s and 3 p orbitals
that's why carbon forms 4 identical bonds in methane
4 bonds point to the corners of tetrahedron
a given number of atomic orbitals hybridizes to form an equivalent number of hybrid orbitals
one 2s and 2 2p orbitals form 3 sp2 hybrid orbitals
BF3. 120 degr
one 2s and one 2p orbitals form sp hybrid orbitals
BeH2. orbitals are oriented 180 degr
one 2s and 3 2p orbitals form 4 sp3 hybrid orbitals
2.Bonding
through bonding, atoms gain a complete outer shell of valence electrons
octet rule
ionic bond - transfer of electrons from one element to another
covalent bond - sharing of electrons between to nuclei
atoms with 1-4 valence electrons form 1-4 covalent bonds respetively.
atoms >=5 valence eletrons form 8 - n val. el.
lone pair :C
7.Determing Molecular Shape
bond length (pm =10^-12m)
bond length decreases as the size of the atom decreases (across a row). bond length increases as the size of the atom increases(down a comumn)
bond angle
VSEPR (valence shell electron pair rupulsion theory)
the most stable arrangement keeps these groups as far away from each other as possible
group - either an atom or lone pair of electrons
ignore multiple bonds in predicting geometry, count only atoms and lone pairs
geometry
2 groups (linear) - 180 degree
3 gr(trigonal linear) - 120 d
4 gr (tetrahedral) - 109.5
solid line is used for a bond in a plane
wedge - for a bond in front of the plaene
dashed wedge - for a bond behind the plane
NH3 is trigonal pyramidal due to lone pair of lectrons (H-N-H - 107 degr). H2O has two lone pairs (H-O-H has 105 degr.) bond angle is smaller that the theoretical one bacause of the repulsion of the lone pairs of electrons
Electronegativity and Bond Polarity
Electronegativity is a measure of an atom's attraction for electrons in a bond
Electronegativity increases across a row of the periodic table as the nuclear charge increases
Electron. decreases down a column as the atomic radius increases, pushing the valence electrons farther from the nucleus
the elcetrons are equally shared if the electron. of atoms is similar. bond is nonpolar (C-H)
C-O unequal sharing of electrons. The bond is polar, or polar covalent
bond is said to have a dipole, a partial separation of charge
electroneg. diff. between two atoms is =>0.5 units
5.Exceptions to the Octet Rule
boron (2 bonds) and beryllium (3 bonds); phosphorus, sulfur (may have more than 8 electrons due to d orbitals; 6, 5 bonds)
10.Ethane, Ethylene, and Acetylene
rotation can occur around central C-C sigma bond
ethylene: sp2 hybridization C=C
sigma bond, formed by end-on overlap of two sp2 hybrid orbitals
a pi bond, formedbyside-by side overlap of two 2p orbitals
rotation does not occur
π bonds are usually weaker and therefore more easily broken than σ bonds.
acetylene: C triple bond C
sp hybrid
one sigma bond nad 2 pi bonds
3.Lewis Structure
electron dot representation of molecules
formal charge = number of VE - number of el. an atom "owns";
"owned el."= num. of unshared electrons + 1/2[num. of shared ones]
Organic Chemistry
Smith
6.Understanding Organic Reactions
Bond Breaking and Bond Making
one or series steps reactions
1-step is called cocerted reaction
startig material converts directly to product
stepwise reaction
starting material converts to reactive intermediate and then to the product
Bond Cleavage
homolytic cleavage(homolysis) - bond breaks and electrons are equally divided between the two atoms
generates uncharged intermediates
to move one electron use "fishhook"
heterolysis(heterolitic cl.) - unequally dividing of the electrons
generates charged interm.
use full-headed curved arrows(one pair)
both require energy
Radicals
double-headed arrow is drawn between resonance structures
Thermodynamics
Bond Dissociation Energy
Kinds of Organic Reactions
The symbols “hm” and “Δ” are used for reactions that require light or heat, respectively
addition
elements are added to a starting material
pi bond is broken, 2 sigma bonds are formed
substitution
atoms or group of atoms is replaced by another one
sigma bond: one breaks and another forms at the same carbon atom
elimination
elements of the starting materials are "lost" and pi bond is formed
2 sigma bonds are broken, 1 pi bond forms between adjacent atoms
E.D. for Two-Step Reaction Mechanism
Enzymes
Catalysts
Enthalpy and Entropy
Energy Diagrams
Kinetics