UNIVERSIDADE FEDERAL DE SÃO CARLOS Fundamentos de Química Orgânica Aula 2 Prof. Marco Antonio B Ferreira [email protected] 3351-­‐8075 www.lqbo.ufscar.br 1 imumthat
stability
(i.e.,
minimum
is rather
achieved
when
nuclei
areLike
a certain
disorbitals
belong
to the
whole energy)
molecule
than
to a the
single
atom.
an atomic
tancethat
apart.
This distance
is the bond
length
of the the
newnucleus
covalentofbond.
The length
orbital
describes
the volume
of space
around
an atom
whereofan
¬likely
H bond
Å. a molecular orbital describes the volume of space around
the H is
electron
toisbe0.74
found,
As Figure
1.2anshows,
energy
is released
when Like
a covalent
forms.
When the
a molecule
where
electron
is likely
to be found.
atomicbond
orbitals,
molecular
orH
¬
H
kcal>mol
bond
forms,
(or
435
kJ
mol)*
of
energy
is
released.
Breaking
the
104
>
bitals have specific sizes, shapes, and energies.
•  Como átomos formam ligações? bond requires
precisely
the
same amount of energy. Thus, the bond strength—also
Let’s look first at the bonding in a hydrogen molecule (H 2). As the 1s atomic orbital
called the bond dissociation energy—is the energy required to break a bond, or the
of one
hydrogen
atom
approaches
theter 1sEvery
atomic
orbitalbond
of avalência second hydrogen
atom,
Segundo Lewis: Busca por sua covalent
camada de completa a energy
released when
a bond
is formed.
has a characteristic
bond
theylength
begin
to overlap.
As the atomic orbitals
move closer together, the amount of overparFr do comparFlhamento de elétrons. and
bond
strength.
lap increases
the orbitals combine
to of
form
a molecular
orbital.
The
covalent
Orbitalsuntil
are conserved—the
number
molecular
orbitals
formed
must
equal bond
the
thatnumber
is formed
when the
twode scombined.
atomic
orbitals
overlapthe
isSEMI-­‐PREENCHIDOS called
a sigma
A
TLV: 2 orbitais atômicos leva a s
of Combinação atomic
orbitals
In describing
formation
of an1S2
bond,
H ¬bond.
H
bond
is formação cylindrically
electrons
in the bond
disde symmetrical—the
um two
novo orbital. however,
we combined
atomic
orbitals,
but discussed
only are
one symmetrically
molecular orbital.
tributed
imaginary
lineorbital?
connecting
the centers
of the two
atoms joined by the
Whereabout
is thean
other
molecular
It is there,
but it contains
no electrons.
s comes
bond. Atomic
(The term
from the
fact different
that cylindrically
symmetrical
ororbitals
can combine
in two
ways: constructively
andmolecular
destructiveEx.: Formação da molécula H2. Ligação bitals
possess
symmetry.)
ly.
They cans
combine
in ade constructive,
additive manner,
just casovalente two lightsigma waves(σ) or
Teoria de Ligação de Valência sound waves may reinforce each other (Figure 1.3). This is called a S (sigma) bonding molecular orbital. Atomic orbitals can also combine in a destructive
way, cancel=
ing each other. The cancellation is similar to the darkness that occurs when two light
wavesHcancel each other
two sound waves
cancel
H or to the silence that occurs when
H H
H H
each other (Figure 1.3). This destructive type of interaction is called a S* antibonding
1s atomic
1s atomic
orbital
molecular
orbital. An
antibonding orbital is indicated by an molecular
asterisk 1*2.
orbital
orbital
Figure
combination
During bond formation, energy is released asconstructive
the two orbitals
start to overlap, be- >
The wave
cause the electron in each atom not onlywaves
is attracted
to
its
own
nucleus
but
also
is
athydrogen
reinforce
+
+
each
resulting
tracted to the positively charged nucleus
ofother,
the other
atom (Figure 1.2). Thus, the reinforce
in bonding
+ nuclei is what (top) or c
attraction of the negatively charged electrons for the positively charged
(bo
holds the atoms together. The more the orbitals overlap, the more the energy decreases other
that inte
nucleus
of the
2 phase,
w
destructi
which model provides the best description of the molecule under discussion. We w
use the VSEPR model in Sections 1.7–1.13.
PROBLEM 14 ◆
E o caso do carbono???? PROBLEM
14 ◆of molecular orbital 1s, s*, p, or p*2 that results when the o
Indicate
the kind
combined
as kind
indicated:
p*2 thatatômicos Indicate the
of a molecular
orbital 1s, s*,
results when
the orbitals ar
Segundo TLV: Combinação de p,
2 or
orbitais SEMI-­‐
aP MP 85:2 3002-30-02 4r950_100-10IURB
combinedPREENCHIDOS as indicated: leva a formação de um novo orbital. a.
a.
C (Z +
= 6) 1s2 2s2 2px1 2py1 c.
c.
+
Lewis +
C + 2H
Geometria angular +
H
C H
H
C H
Temos aqui uma falha no modelo . cimota p2
latibro
++
ygrenE
b.b.
. d. d.
. . +
+Como fica o formato desta ligação σ ligante C-­‐H? 1.7 Bonding
Bonding in
and
Ethane:
Single
Bonds
1.7
inMethane
Methane
and
Ethane:
Single
B
We will begin the discussion of bonding in organic compounds by looking at the
bon
3 mWe
gnidwill
nobitnabegin
.demrdiscussion
of
*s ehT the
of bonding in organic compounds by looking a
length and
all the
bondand
angles
are the same (109.5°), we can conclude that th
nd a carbon–carbon
bond),
inC ¬
Methanedouble
four covalent
(CH 4) has
H bonds. Because all four bonds have the same
bonds
in
methane
are
identical.
C
¬
H
carbon–carbon
triple
length
and bond).
all the bond angles are the same (109.5°), we can conclude that the four
Four
different
to
represent
a methane molecule are shown here.
E commonly
o care
aso do carbono???? oms other than
carbon
that
areways
in methane
identical.
C¬
H bonds
Four different
to represent a methane molecule are shown here.
d by oxygen, nitrogen,
andways
the halogens.
determine the bond angles
in a molecule,
H
s in a molecule, weHcan figure out which
H
H
C
C
H
H
109.5°
nds. Because all four bonds
have
the same
HH 109.5°
formula
ball-and-stick
space-filling
model
perspective
formula
ball-and-stick
model model space-filling
model
electrostatic
(109.5°), weperspective
can conclude
that the four
of
ofmethane
methane
of methane
of methane
of methaneof methane map for m
aaperspective
bonds
in thein
plane
the paper
arepaper
drawnare
as solid
lines,
e molecule are In
shown
here. formula,
In
perspective
formula,
bonds
the of
plane
of the
drawn
as solid
Todos o
s bonds protruding out of the plane of the paper toward the viewer are drawn as solid
bonds
protruding
out of the plane of the paper toward the viewer are drawn a
comprimentos de protruding
wedges, and those
back from the plane of the paper away from the viewer
wedges,
and
those
protruding
back from the plane of the paper away from the
ligação iguais are drawn
as hatched wedges.
are
as hatched wedges.
d drawn
= 1,10 model
e
C-­‐H
Molécula apolar EletronegaFvidade C e H semelhantes Carbono tetraédrico space-filling model
of methane
electrostatic potential
map for methane
ane of the paper are drawn as solid lines,
4 an electron, an extra 210 kcal>mol (or 879 kJ> mol) is re
tion is energetically advantageous (Figure 1.9).
......usando hibridização pAs
ara explicar a valência e a result
of electron
promotion,
forms four covalent bonds
geometria do carbono!!!! carbon
and releases 420 kcal> mol of
energy. Without promotion, carbon
would form two covalent bonds
and release 210 kcal> mol of energy.
Because it requires 96 kcal> mol to
promote an electron, the overall
energy advantage of promotion is
114 kcal>mol.
Potential energy
Figure 1.9 N
promotio
96 kcal/m
We have managed to account for the observation th
April, 1931
NATURE OF THE CHEMICAL BOND
C¬H
bonds, but whatTHEaccounts
for the fact that the four1367
Linus Carl Pauling (1901–1994)
[CONTRIBUTION
CHEMICAL
LABORATORY,
OF any
was born in Portland, Oregon. A
Å, and INSTITUTE
cal? EachFROM
hasGATES
a bond
length
of 1.10CALIFORNIA
breaking
TECHNOLOGY,
No. 2801
friend’s home chemistry laboratory
same amount
of energy (105 kcal> mol, or 439 kJ> mol).
THE NATURE OF THE CHEMICAL BOND.
sparked Pauling’s early interest in
threeAPPLICATION
p orbitals to
these
four bonds,
OFform
RESULTS
OBTAINED
FROMthe
THEbond form
science. He received a Ph.D. from the different
QUANTUM
AND FROM
A THEORY
fromMECHANICS
the three bonds
formed
with p OF
orbitals. H
PARAMAGNETIC SUSCEPTIBILITY TO THE STRUCTURE
California Institute of Technology
tical bonds, using OF
oneMOLECULES
s and three p orbitals? The answ
and remained there for most of his
orbitals.
BY LINUSPAULING
academic career. He received the
RECEIVED
FEBRUARY
17,1931
APRIL6, 1931
Hybrid
orbitals
are mixedPUBLISHED
orbitals—they
result from
Nobel Prize in chemistry in 1954 for
Duringof
thecombining
last
yearsorbitals,
the1931, problem
ofpp the
nature of hybridizatio
the chemical
J. Afour
m. Chem. Soc., 53 called
(4), 1367–1400 cept
orbital
his work on molecular structure. Like bond
has been attacked by theoretical physicists, especially Heitler and
Pauling
in 1931.
If the
one
s andmechanics.
three p orbitals
of
application
of the
quantum
This work 5 hasthe
Einstein, Pauling was a pacifist, win- London, by the
ledthen
to an apportioned
approximate theoretical
calculation
of the
energy of each
formation
into four
equal
orbitals,
of and
the fou
1.15
1.15 BONDING
BONDINGININMETHANE
METHANEAND
ANDORBITAL
ORBITALHYBRIDIZATION
HYBRIDIZATION
In the 1930s Linus Pauling offered an ingenious solution to the puzzle. He began
1.15
BONDING
INearly
METHANE
AND
HYBRIDIZATION
with
simple
idea:
“promoting”
one
of theORBITAL
2s
electrons
to
the concerned
empty
2pz orbital
gives
AAvexing
vexingpuzzle
puzzle
inainthe
the
early
days
daysofofvalence
valence
bond
bond
theory
theory
concerned
thethe
bonding
bondinginin
±
four half-filled orbitals and allows for four C H bonds (Figure 1.20b). The electron
methane
methane
(CH
(CH
).4configuration
).Since
Since
covalent
bonding
bonding
the
theoverlap
overlap
of
ofhalf-filled
half-filled
orbitals
orbitals
ofof
the
1 requires
1 requires
A vexing
in covalent
the
early
days
theory
concerned
the
bonding
inthe
4puzzle
that
results
(1s22sof
2pxvalence
2py12pz1),bond
however,
is inconsistent
with the
fact
that
2 22 2 1 1 1 1
all
ofSince
these bonds
arean
equivalent
and
directed
toward
theofcorners
of2s2p
a tetrahedron.
The
connected
connected
atoms,
carbon
with
with
an
electron
electron
configuration
configuration
of1sof1s2s
2p
hasonly
only
two
two
methaneatoms,
(CH
covalent
bonding
requires
the
overlap
half-filled
of
the
x 2p
x 2p
yorbitals
yhas
4).carbon
2
2
1
1
second
part
of
Pauling’s
idea
was
novel:
mix
together
(hybridize)
the
four
valence
......usando hibridização ara ecan
xplicar bonds
valência connected
atoms,
carbon1.20a),
with
anp
configuration
of
1sto2s
2p
2pe
half-filled
half-filled
orbitals
orbitals
(Figure
(Figure
1.20a),
soelectron
sohow
how
canit ithave
havea
bonds
tofour
four
hydrogens?
x hydrogens?
y has only two
Hibridização orbitals of carbon (2s, 2p , 2p , and 2p ) to give four half-filled orbitals of equal energy
geometria do metano!!!! because they come from one s orbital and three p orbitals.
Energy
Energy
Energy
x
y
z
half-filled orbitals
howincan
it have
bonds
to four
hydrogens?
(Figure (Figure
1.20c). The1.20a),
four newso
orbitals
Pauling’s
scheme
are called
sp3 hybrid
orbitals
Figure 1.21 depicts some of the spatial aspects of orbital hybridization. Each sp3
2p2p
hybrid orbital has two lobes 2p
of 2p
unequal size, making the electron density greater on one
2p side of the nucleus than the other.
2p In a bond to hydrogen, it is the larger lobe of a carbon sp3 orbital that overlaps with a hydrogen 1s orbital. The orbital
3 3 overlaps corre2sp
2sp
3 1.22. Orbital oversponding to the four C±H bonds of methane are portrayed in Figure
2sp
lap along the internuclear axis generates a bond with rotational symmetry—in this case
promoção a C(2sp3)±H(1s)
! bond. A tetrahedral arrangement of four ! bonds is characteristic
3
of sp -hybridized carbon.
3
The peculiar shape of sp2s
hybrid orbitals turn out to have an important consequence.
2s2s
2s
2s Since most of the electron density
2s in an sp3 hybrid orbital lies to one side of a carbon
atom, overlap with a half-filled 1s orbital of hydrogen, for example, on that side produces
3 3
3 sphybrid
hybrid
a stronger
bond than would result
otherwise.
If
the electron probabilities were
equal
on
Ground
Ground
electronic
electronic
Higher
Higher
energy
energy
electronic
electronic
hybrid
spsp
Ground
electronic
Higher
energy
electronic
both
sides
of
the
nucleus,
as
it
would
be
in
a
p
orbital,
half
of
the
time
the
electron
would
state
state
of
of
carbon
carbon
state
state
of
of
carbon
carbon
state
state
of
of
carbon
carbon
state of carbon
state of carbon
state of carbon
be remote from the region between the bonded atoms, and the bond would be weaker.
Thus,
not only does Pauling’s orbital hybridization
proposal account for carbon forming
(a)(a)
(b)
(b)
(a)
(c)(c)(c)
(b)
four bonds rather than two, these bonds are also stronger than they would be otherwise.
FIGURE
FIGURE
FIGURE
1.2
configura
configu
configuratio
itsitsmost
mos
its most stab
electron
electron
i
electron is “p
the
the2s2sor
the 2s orbita
2p2p
orbita
orbi
2p orbital. (c
and
and
the
the
t
and the thre
combined
combin
combined
to
four
four
e
four
equa
hybridize
hybridio
hybridized
which
which
con
c
which
contai
Neste caso, os orbitais não apontam Combine one 2s and three 2p orbitals to give four equivalent sp hybrid orbitals:
para os cantos de um tetraedro. 3
y
y
"
y
"
"
!
x
y
x
!
x
!
z
z
2s
z
2 px
x
"
z
2 py
2 pz
6 Section 1.7
Bonding in Methane and Ethane: Single Bonds
......orbitais híbridos sp : 4 orbitais atômicos geram 4 orbitais híbridos. 3p orbital
with one s orbital to form the hybrid orbitals.)
Each sp 3 orbital has the
25%s orbital
s character
subtracts from
3
the
lobe
of
the
and 75% p character. The four sp orbitals are degenerate—they have the same energy.p orbital
p
p
p
hybridization
s
sp 3
hybridization
4 orbitals are hybridized
sp 3
sp 3
> Figure 1.11
sp 3
An s orbital and th
hybridize to form
An sp3 orbital is m
stable than a p orb
stable as an s orbit
hybrid orbitals
Like a p orbital, an sp 3 orbital has two lobes. The lobes differ in size, however, because the s orbital
p adds to pone lobe ofpthe p orbital3 and subtracts from the other lobe of
the p orbital (Figure 1.10). The stability of an sp orbital reflects
itsp
is3
sp 3its composition;
sp 3
more stable than a p orbital, but not as stable as an s orbital (Figure 1.11). The larger
lobe of the sp 3 orbital is used in covalent bond formation.
s
the s orbital adds to
the lobe of the p orbital
sp 3
> Figure 1.10
The s orbital adds to one lobe of
The four sp 3 orbitals arrange themselves in space in a way that allows themthetopget
orbital and subtracts from t
other lobe of the p orbital.
as far away from each other as possible
s orbital (Figure 1.12a). This occurs because electrons
repel each other and getting as far from each other as possible minimizes the repulsion
(Section 1.6). When four orbitals spread themselves into space as far from each other
as possible, they point toward the corners of a regular tetrahedron (a pyramid with four
p orbital
a.
b.
H
the s orbital subtracts from
lobe of 1.12
the p orbital
>theFigure
(a) The four sp3 orbitals are
directed toward the corners of a
Figure 1.11
7 tetrahedron, causing each >bond
An s orbital and three p orbitals
angle to be 109.5°.
3
as far
away 1.6).
fromWhen
each four
otherorbitals
as possible
(Figure
1.12a).
This
1.16 sp3spread
Hybridization
and Bonding into
in Ethane
(Section
themselves
space
repel
other
andpoint
getting
as the
far corners
from each
possible
aseach
possible,
they
toward
of a other
regularastetrahedro
(Section 1.6). When four orbitals spread themselves into spaF
b
as possible, they point toward the corners of a regular tetrahed
in
Going away
from you
a.
a.
Coming
toward you
b.
In the plane
of the paper
C In the plane
of the paper
H
(a) The foc
H(1s)±C(2sp3)
directed tc
" bond
> Figuh
H
b.
C
> Figurea
H
H
H
H
C
C
H
109.5!
H
CH
H
H
4 ligações σ iguais. H
1. Você consegue tetrahedr
t
(a) The
angle
to cb
directed
(b)
An orb
lo
tetrahest
showing
angleoftu
orbital
t
orbital
ofw
(b) An
o
the
smalle
t
showin
orbitals
orbitalar
orbital
the sma
orbitals
Distribuição espacial dos orbitais desenhar esta PROBLEM 1.20 Construct an orbital diagram like that of Figure 1.20 for nitrokind of orbital is the
gen in ammonia, assuming sp3 hybridization. In whatestrutura? unshared pair? What orbital overlaps are involved in the N±H bonds?
8 form
four
covalent
bonds:
C¬
C
of 109.5°,
and
of
the
bond
isC1.54
Ethane,
like met
3bond.
ethane
3the
3
C
¬H
C¬
thethes Corbital
of a Each
hydrogen
to
form
a3 length
Thus,
the
bondÅ.
issp
sp
¬
C
bond.
of
the
remaining
three
orbitals
of
each
carbon
overlaps
sp
–sp
C
¬
H
–s
formed
by
overlap,
and
each
bond
is
formed
by
overlap
the s orbital 3of a3 nonpolar
hydrogen molecule.
to form a C ¬ H bond. Thus, the C ¬3C bond is
sp –sp
Hbond
–s
sp
formed
by
and
each
bond
is
formed
overlap
3 EachC
3nearly
(Figure
1.13).
angles
in
ethane
isby
the
tetrahedral
bond to
angle
Cthe
¬
C
¬3–s
C
the
s
orbital
hydrogen
to spform
aCof¬
bond.
Thus,
is carbon
3of a3 overlap,
sp
orbital
of
one
carbon
overlaps
anthe
orbital
ofbond
the other
¬
H Hbond
sp
formed by sp 3–sp 3 overlap, One
and
each
is
formed
by
overlap
Hisform
H
3 bond
3 sp
C
¬
C
Å.
ofbond
109.5°,
and
the
length
of
the
bond
is
1.54
Ethane,
like
methane,
a
(Figure
1.13).
Each
of
the
angles
in
ethane
is
nearly
the
tetrahedral
angle
sp
–sp
C
¬
H
–s
formed
by
overlap,
and
each
bond
is
formed
by
overlap
¬ C bond.
the Cangles
Each ofisthe
remaining
three sp orbitals
ofangle
each carbon overlaps
(Figure 1.13). Each of thenonpolar
bond
in
ethane
nearly
the
tetrahedral
bond
molecule.
C ¬like
H bond.
thethe
s angles
orbital
of
a hydrogen
toÅ.form
Thus,
the
CC¬
C
ofof(Figure
109.5°,
and
is
1.54
Ethane,
methane,
isaH
aC ¬CC bond
1.13).
Each
of theof
bond
inbond
ethane
is nearly
theatetrahedral
bond
angle
C isH
¬
C
Å.
109.5°,
andthe
thelength
length
of
the
is
1.54
Ethane,
like
methane,
is
3 bond
3
3
spC–sp
C ¬ Hlike
by¬
overlap,
bond
is formed
H formed
of 109.5°,
the length
of the C
bond
is 1.54andÅ.each
Ethane,
methane,
is by
a sp –s overlap
nonpolar
molecule.
Hand
109.6°
°
nonpolar
molecule.
1.10
A
(Figure 1.13). Each of the bond angles in ethane is nearly the tetrahedral H
bondH
angle
nonpolar
molecule.
H
H
109.6° H
°
of 109.5°, and the length of the C ¬ C bond is 1.54 Å. Ethane, like methane,
1.10 A
ethane is a
C
C
nonpolar
molecule.
H
H
H
C
C
109.6° H
H 109.6°
H
H 109.6° H
° H A° H H
HH
H 1.54
HA
1.54
H
109.6°
°
C C CC
1.10 A
H
perspective
formula
perspective formula
C
C
H
of ethane
C
C
of
ethane
H
° °HH
HH1.54
1.54AA
° H
H 1.54 A
° H
One sp 3 orbital of one carbon overlaps an sp 3 orb
the C ¬ C bond. Each of the remaining three sp 3 or
model
ball-and-stick model
space-filling
model
ball-and-stick
Celectrostati
¬ H bo
the s model
orbital space-filling
of ofa ethane
hydrogen
toelectrostatic
form
apotential
map for ethane
of ethane
of
ethane
map for
of ethane
3
3
formed by sp –sp overlap, and each C ¬ H bond
H 1.54
A
space-filling
model
electrostatic
potential
ective2) formula
ball-and-stick
(Figure model
1.13). Eachelectrostatic
of the bond
angles in ethane is ne
Por que ligação C-­‐C é mmodel
aior que C-­‐H? space-filling
potential
spective
formula
ball-and-stick
model
space-filling
model
electrostatic
potential
rspective
formula
ball-and-stick
model
of
ethane
map
for
ethane
of
ethane
of
ethane
space-filling
electrostatic potential
perspective
formula
ball-and-stick model
mapmodel
for ethane
of ethane
of ethane
H
H
¬
C bond is 1.54
of
109.5°,
and the
length
the C
ethane
map forof
ethane
of ethane
ofofethane
of ethane
map forHethane
ethane
of of
ethane
H
nonpolar molecule.
H
H
H
H
HH
H
H
HH
H
CC
C
HHH
HHHC
H
C
H
H
H
H 109.6° H
°
1.10H A
C HH
C H
H
H H
H
C
CH
C
C
CC H
C
▲ Figure 1.13
H
H
H
H
CC
C
H
HHH
H
HH
CC
C
H
H
σ (C(sp3)-­‐C(sp3)) C
HH
CH
C
H
H
C
C
H
C
An orbital picture of ethane. The C ¬ C bond is formed by sp3–sp3 H
overlap, andHeach C
H¬ H
°
3
3
(sp3)
(1s)
H
H
1.54
A
sp
–s
bond
is
formed
by
overlap.
(The
smaller
lobes
of
the
sp
orbitals
are
not
shown.)
HH
H
H
σ (C
-­‐H
) H
HH
H
H
H
space-filling m
perspective
formula
ball-and-stick
model
HHH
▲ Figure 1.13
of ethane
of ethane
of ethane
▲ Figure
1.13 picture
An orbital
of ethane. The C ¬ C bond is formed by sp3–sp3 overlap, and each C ¬ H
3 not3shown.)
3
Figure1.13
1.13
–s overlap.
bondpicture
is formedof
by sp
(The
smaller
lobes
of formed
the sp3 orbitals
are
An orbital
ethane.
The
C3) ¬
C3 ocê bond
is
by sp
–sp overlap, and e
V
c
onsegue ▲▲▲
Figure
Figure
1.13
3
3is formed by sp 33–sp 33 overlap, and each C ¬ H3
An
orbital
picture
of
ethane.
The
C
¬
C
bond
sp is–s
bond isThe
formed
overlap.
(The
lobes
the
spHHorbitals are not sh
¬
AnAn
orbital
picture
ofof
ethane.
CC¬¬CCby
bond
by
overlap,
and of
each
sp3 –sp
CC¬
orbital
picture
The
bond
isformed
formed
by sp
–spsmaller
overlap,
and
each
3ethane.
desenhar eare
sta estrutura? sp3 3–soverlap.
bondisisformed
formedby
bysp
overlap. (The smaller
smaller lobes of
of the
sp 33 orbitals
bond
arenot
notshown.)
shown.)
–s overlap.(The
bond is formed
by sp–s
(The smallerlobes
lobes ofthe
the sp
sp orbitals
orbitals are
not
shown.)
H
H
9 bonded to only three atoms:
A Dupla ligação H
......usando hibridização para explicar a geometria do eteno. (b)
2p
2p
H
C
C
H
H
ethene
(ethylene)
2p
To bond to three atoms,
each carbon hybridizes th
2sp
orbitals (an s orbital and two of the p orbitals) are hy
obtained. These are called sp 2 orbitals. After hyb
three degenerate sp 2 orbitals and one p orbital:
Energy
2
2s
2s
Ground electronic
state of carbon
(a)
p
Higher energy electronic
state of carbon
s
(b)
p
sp2 hybrid
state of carbon
p
hybridization
(c)
FIGURE 1.25 (a) Electron configuration of carbon in its most stable state. (b) An electron is
three
orbitals
are
hybridized
Aqui temos a hibridização dos three
orbitais: “promoted” from the 2s orbital to the vacant
2p orbital.
(c) The
2s orbital
and two of the
2
2p orbitals are combined to give a set of three equal-energy sp -hybridized
2s + 2pxorbitals.
+ 2py One of
the 2p orbitals remains unchanged.
2
To minimize electron repulsion, the three sp
10 orb
In general, you can expect that carbon will be sp2-hybridized when it is directly
bonded to three atoms.
z
z
z
x
x
x
y
y
z
y
x
y
Leave this
orbital alone
Combine one 2s and two 2p orbitals
z
x
!
3
y
2
Three sp hybrid orbitals
2 pz
FIGURE 1.26 Representation of orbital mixing in sp2 hybridization. Mixing of one s orbital
with two p orbitals generates three sp2 hybrid orbitals. Each sp2 hybrid orbital has one-third s
2
11 carbon–
in ethylnt and a
compoerlap of
ls along
. The "
from a
of 2p
Begin with two sp2 hybridized carbon atoms and four hydrogen atoms:
Half-filled 2p
orbital
H
H
sp2
sp2
C(2sp2) – C(2sp2) ! bond
sp2
H
sp2
sp2
In plane of
paper p orbitals
sp2
H
that remain on carbons
overlap to form " bond
sp2 hybrid orbitals of carbon
overlap to form ! bonds to
C(2p) – C(2p)
hydrogens and to each other
C(2sp2) – H(1s)
! bond
" bond
C(2sp2) – C(2sp2) ! bond
1.18
sp HYBRIDIZATION AND BONDING IN ACETYLENE
One more hybridization scheme is
p orbitals that remain on carbons
overlapin
to form
" bond chemistry.
important
organic
It is called 12 sp
scarbon.
bond
andother
the is
other
is a pAll
bond.
C ¬ are
H bond
e a plane, it is called a trigonal planar
s bond
and the
a p bond.
the CAll
¬ the
H bonds
sb
2
ular to the plane defined by the axes of the sp
σ bond
formed
σ bond
formed
b.
2
2
by sp
–sp
s called
overlap
This
a double
byis
– s overlap
a.a.
onds with each other.
H Hbond are not identical. One H
n the double
of theH
2
orbital of one carbon with an sp orbital of the
ond because it is formed by end-on overlap H
C
C
her two sp 2 orbitals
to
of a
C
C overlap the s orbital
H
The second carbon–carbon bond results from
idized p orbitals.
Side-to-side
of Hp orσ bond formedoverlap
by
H
2σ
2 overlap
– sp
bond
bybond is aH
H of thespbonds
b). Thus, one
informed
a double
2 – sp2 overlap
he C ¬ H bonds are sspbonds.
b.
π bond π bond
c.
c.
H
H
H
C
H
C
C
H
H
C
C
σ bond
H
H
σ bond
▲ Figure 1.16
(a) One
C ¬ C bond
in ethene is a s bond formed by sp2–sp2 overla
▲
Figure
1.16
2
π bond
are formed
by
overlap.
The second
is a by
sp
¬ C bond
p bond
sp2–
(a) One C ¬ –s
C bond
in (b)
ethene
is a s Cbond
formed
overlap of a p orbital of2 one carbon with a p orbital of the other ca
are formed by sp –s overlap. (b) The second C ¬ C bond
accumulation
of electron density above and below the plane conta
H of
overlap
a p orbital of one carbon with a p orbital of t
and four hydrogens.
c.
H
H
C
H
σ bond
H
3-D Molecule:
Ethene
3-D Molecule:
accumulation of electron density above and below the p
and four hydrogens.
CThe two p orbitals that overlap to form the p bond must be
for maximum overlap to occur. This forces the triangle form
The twotoplie
orbitals
form
the pforme
bon
two hydrogens
in the that
sameoverlap
plane astothe
triangle
overlap
to occur.
forcesofthe
tria
H
and for
two maximum
hydrogens.
This means
that allThis
six atoms
ethene
hydrogens
to lie
in the occupy
same plane
as the
trian
andσtwo
the
electrons
in the
p orbitals
a volume
of space
bond
planeand
(Figure
1.16c). The electrostatic
mapatoms
for etho
two hydrogens.
This meanspotential
that all six
13 nonpolar
molecule
with in
an accumulation
negativeacharge
(t
and the
electrons
the p orbitalsofoccupy
volume
4.) Você consegue desenhar estas estruturas? 5) Desenhe o eteno em ao menos 3 perspec:vas diferentes!!!! 6) Agora escolha uma que vc consiga desenhar todos os orbitais envolvidos nas ligações C-­‐H e C=C. 14 that accompanies the chapter.
egative charge would be
foundcharge
on the
otherbeside.)
negative
would
found on the other side.)
Bonding in Ethane
3
H The two carbon atoms in ethane are tetrahedral. Each carbon uses four sp orbital
form four covalent bonds:
116.6°
H H
H 121.7°
H
°
1.08 A
116.6°
H
sts of
π bond
C
C
°
H 1.33 A
H
H
a double bond consists of
one σ bond and one π bond
ball-and-stick model
of ethene
C
C
H
model
H
H space-filling
of ethene
electrostatic pot
for ethe
ethane
ball-and-stick model
space-filling model
electrostatic potential map
of ethene One sp 3 orbital of one
ofcarbon
ethene
forofethene
overlaps an sp 3 orbital
the other carbon to fo
the C ¬ C bond. Each of the remaining three sp 3 orbitals of each carbon overl
the s orbital of a hydrogen to form a C ¬ H bond. Thus, the C ¬ C bond
7) Compare os comprimentos de Densidade negaKva na ligação formed by sp 3–sp 3 overlap, and each C ¬ H bond is formed by sp 3–s ove
ligação (C-­‐H) e (CC), explicando as of the bond angles in ethaneC=C denota aior (Figure
1.13). Each
is nearly
them
tetrahedral
bond an
diferenças observadas entre and
o ethe
:leno concentração eletrônica m of 109.5°,
length of the C ¬ C bond
is 1.54 Å. Ethane,
likeemethane,
nonpolar molecule.
e o etano. decorrência da ligação π. H 109.6° H
°
1.10 A
H
C
C
H
° H
H 1.54 A
perspective formula
of ethane
Força de ligação: C=C: 152 kcal/mol C-­‐C: 88 kcal/mol ball-and-stick model
of ethane
space-filling model
of ethane
electrostatic poten
map for ethane
15 H
H
Algumas estruturas interessantes envolvendo apenas os átomos de carbono. 8) Dê o nome de cada um dos compostos. Dê também a hibridização dos átomos de carbono em cada caso. 16