Jumat, April 09, 2010

kimia organik

1
Kimia Organik
1. Structure and Bonding review (11/11)
2. Classes of Organic Compounds (11/11)
3. Aliphatic Hydrocarbons (11/11)
4. Aromatic Hydrocarbons (18/11)
5. Chemistry of the Functional Groups (25/11-
9/12):
• Alcohol & Ethers
• Aldehyde & Ketones
• Carboxylic Acids & derivates
6. Chemical Analysis and Instrumentation (an
Introduction) (16-23/12)
Introduction
Organic chemistry is the chemistry of the compounds of
carbon.
Inorganic Chemistry: the chemistry of the other ~100
elements.
Carbon can form more compounds due to its ability to form
not only single, double or triple C-C bonds, but also to link up
with each other in chains and ring structures.
Over 13 million synthetic and natural organic compounds are
known – significantly greater than so known inorganic
compounds
Organic chemicals, those from living organisms (animal,
vegetable) were complex and contained C, H, and often N
and/or O.
Inorganic chemicals (mineral) were simpler, could contain a
variety of elements, but only rarely carbon, except for
carbonates.
covalent bonding
- sharing electrons
- most common bonding in organic compounds
2
How to handle variety
nomenclature - clear methods for
naming structures and reactions
structures - organized by functional
groups
reactions - organized by reaction
types (what happens?)
reactions - organized by reaction
mechanisms (how does it happen?)
Classes of organic compounds
distinguished according to functional
groups they contain
a functional group is a group of atoms
that is largely responsible for the
chemical behavior of the parent
molecule
all organic compounds are derived
from hydrocarbons because they are
made up of only H and C
3
Classes of organic compounds
aliphatic hydrocarbons do not contain benzene
group/ring
aromatic hydrocarbons contain one or more
benzene rings
Hydrocarbons
Aliphatic Aromatic
Alkanes Cycloalkanes Alkenes Alkynes
Structure and Bonding review
4
Resonance
more than one possible Lewis
structure for a compound
What's the best Lewis structure?
follow the octet rule
electronegativity determines the best
place to locate charges
carbon monoxide (CO)
nitromethane (CH3NO2)
Resonance structure
If one can draw more than one
reasonable Lewis structure for a
molecule, then that molecule is a
hybrid of the structures which may be
drawn.
Each contributing Lewis structure is a
resonance or canonical structure.
5
Resonance Rules
1. All nuclei must be in the same
location in every resonance structure;
they cannot move.
2. Each resonance structure must have
the same number of unpaired
electrons (eg, 0, 1, 2, etc.).
Molecular Geometry From Lewis Structures –
electron pair repulsion model
Count the number of "electron
groups" around the atom. Each
unshared pair counts as one group,
as does each bond whether single
or multiple.
If there is more than one resonance
structure, use the one with the greater
number of bonds attached to the atom
in question.
6
sp3
sp2
sp
Functional Groups
characteristic arrangement of atoms that define
a family of compounds
R represents generic carbon group
alcohols: R-O-H
ethers: R-O-R
carbonyl group ( C=O )
aldehydes: RCHO
ketones: R2CO
carboxyl group ( COO )
7
Polar Bonds to Carbon
C-C bonds are nonpolar
C-H bonds are generally considered
nonpolar
C-X bonds are polarized with carbon
d+
for X = F, Cl, Br, I, O, S, N
C-M bonds are polarized with carbon
dfor
M = metals
Writing Organic Structures
Lewis structures
- all electrons shown
Kekule structures
- show bonds as lines
- lone pairs sometimes omitted
line structures
- omit lone pairs
- omit hydrogens on carbons
- omit carbons
(assumed to be at the end of every bond)
8
3-Dimensional Structures
dotted-line / wedge
ball-and-stick
space-filling
Visualizing chemical structures
name (common or systematic)
condensed formula (as usually typed out)
Lewis structure (all atoms and bonds
shown)
line structure (omit hydrogens, assume
carbons at vertices)
3-D structure (show bond orientations)
ball-and-stick structure (like a molecular
model you could make)
space-filling model (approximates full size
of electron distribution)
9
Metana, CH4
Cari penggambaran struktur bensen dan penisilin
Alkanes (alkana)
general formula: Cn H2n+2 , n=1,2, …..
only single covalent bonds are present
also known as saturated hydrocarbons
because they contain the maximum number of
hydrogen atoms that can bond with the
number of carbon atoms present
Carbons are sp3 hybridized.
Bonds are σ-bonds. C-C bonds ~ 1.54Å; C-H
bonds ~ 1.10Å. Bond angles ~ 109o.
10
CH4, methane (metana)
the simplest alkane
natural product of the anaerobic
bacterial decomposition of vegetable
matter under water --- marsh gas
Termites are a natural source of
methane by digestively breaking down
cellulose (from wood) – estimated 170
million tons production annually
Sewage treatment processes also
produced methane
Commercially obtained from natural gas
Natural gas is a mixture of methane,
ethane, and small amount of propane
The structure of methane, ethane and
propane are straightforward – there is
only one way to join C atoms
Butane, C4H10 has 2 possible bonding
schemes �� structural isomers n-butane
and isobutane
11
isomers
Structural isomer: molecules that
have the same molecular formula but
different structures
in the alkane series, as the number of
C atoms increases, the number of
structural isomers increases rapidly
butane – 2 isomers; decane (C10H22)
– 75 isomers and C30H62 has over
than 4x108 isomers
Tentukan berapa isomer struktur pentana, C5H12 dan gambar
strukturnya
The first 10 Straight-Chain Alkanes
Dekana CH3 – CH2 - CH3 10 -29,7 174,0
Nonana CH3 – CH2 - CH3 9 -53,5 150,8
Oktana CH3 – CH2 - CH3 8 -56,8 125,7
Heptana CH3 – CH2 - CH3 7 -90,6 98,4
Heksana CH3 – CH2 - CH3 6 -95,3 68,7
Pentana CH3 – CH2 - CH3 5 -129,8 36,1
Butana CH3 – (CH2)2 - CH3 4 -138,3 -0,5
Propana CH3 – CH2 - CH3 3 -189,7 -42,1
Etana CH3 - CH3 2 -183,3 -88,6
Metana CH4 1 -182,5 -161,6
BP
(oC)
MP
(oC)
number
of C
name formula
12
Alkane nomenclature
based on recommendation of the International Union of Pure and
Applied Chemistry (IUPAC)
1. Nama utama berdasarkan rantai karbon terpanjang
2. Rantai alkana kekurangan 1 atom H disebut gugus
alkil, rantai cabang disebut gugus alkil
3. Jika 1 atau lebih atom H diganti gugus lain, nama
senyawa harus menunjukkan lokasi atom C tempat
penggantian tersebut
4. Pemberian nomer atom C rantai karbon terpanjang
sedemikian rupa sehingga memberikan nomer lebih
kecil untuk semua atom C bercabang
5. Jika ada lebih dari 1 cabang alkil yang sama
digunakan awalan di-, tri-,tetra-, … mengikuti nama
alkil.
6. Jika ada 2 cabang alkil berbeda, diberi nama sesuai
gugus alkil diawali dengan nomer atom C posisi
cabang tersebut
7. Penamaan dengan cabang unsur mengikuti aturan
nomer 6
Common alkyl groups
t-butil
Isopropil
n-butil - CH2 – CH2 - CH2 - CH3
n-propil - CH2 - CH2 - CH3
Etil - CH2 - CH3
Metil - CH3
Nama Rumus
CH3
- C – CH3
CH3
- C - H
CH3
13
Functional groups
- CH = CH2 Vinil
- NO2 Nitro
-I Iodo
-Br Bromo
-Cl Kloro
-F Fluoro
- NH2 Amino
Gugus fungsional Nama
Beri nama senyawa berikut sesuai
IUPAC
Gambarkan struktur senyawa 2,2-
dimetil-3-etilpentana
CH3
CH3 – C – CH2 – CH – CH2 – CH3
CH3
CH3
14
Aliphatic hydrocarbon
• alkanes
• cycloalkanes
• alkenes
• alkynes
Struktur
proyeksi
Newman
proyeksi
Sawhorse
15
Reaksi kimia alkana
• Pembakaran
– sangat eksotermis
• Halogenasi alkana ��
alkil halida
– substitusi 1 atau lebih
atom H oleh atom
halogen
• campuran gas metana
dan klor dipanaskan di
atas 100 oC atau diiradiasi
cahaya dengan λ tertentu
4( ) 2( ) 2( ) 2 ( ) 2 2 g g g l CH + O →CO + H O ΔH 0 = −890,4kJ
2 6( ) 2( ) 2( ) 2 ( ) 2 7 4 6 g g g l C H + O → CO + H O ΔH 0 = −3119kJ
4( g ) 2( g ) 3 ( g ) ( g ) CH + Cl →CH Cl + HCl
metil klorida
3 ( g ) 2( g ) 2 2 (l ) ( g ) CH Cl + Cl →CH Cl + HCl
Jika tersedia gas klor berlebih:
metilen klorida
2 2 ( g ) 2( g ) 3(l ) ( g ) CH Cl + Cl →CH Cl + HCl
kloroform
Apakah nama sistematik (sesuai aturan penamaan) untuk metil klorida, metilen klorida
dan kloroform?
RH + X ⎯U⎯V /⎯pa⎯nas→RX + HX
2
Alkil halida
• Kloroform
– cairan volatil untuk anastesi
– toksik thd ginjal, hati dan jantung �� dilarang
• Karbon tetraklorida
– cairan pembersih �� noda minyak pada kain
– toksik
• Metilen klorida
– solven untuk de-kafeinasi kopi dan pembersih
cat
• Klorofluoro karbon
16
Sikloalkana
• Definisi: alkana yang rantai karbon dihubungkan
sebagai suatu cincin
• Rumus umum: CnH2n, n= 3,4,…..
• Yang paling sederhana adalah siklopropana
• Merupakan kandungan kimia senyawa
kolesterol, testosteron, dan progesteron
• Mempunyai 2 geometri berbeda
– chair
– boat
chrysanthemic acid
penarik serangga
cortisone (a steroid)
strain pada sikloalkana
sudut dalam poligon = 180(n-2)/n, n jumlah sisi poligon (von Baeyer)
in fact, prediksi Baeyer BENAR untuk cincin 3 dan 4 yang mempunyai
energi stabilisasi lebih tinggi daripada cincin 5 atau 6 TETAPI geometri
cincin >5 bukanlah PLANAR,sudut dalam C>5 mendekati sudut ideal
tetrahedral, 109o �� C5 dan C6 banyak ditemui secara natural
C5
C6 C8
17
Penamaan sikloalkana
metil siklopentana 1 siklo propil butana
18
Penamaan sikloalkana
1,3 dimetil sikloheksana 1,5 dimetil sikloheksana
NOT
alkena
• disebut juga olefin
• mempunyai sekurang-kurangnya 1 ikatan
rangkap C=C
• Rumus umum Cn H2n n=2,3,4,……
• Alkena paling sederhana : C2H4 (etilen
atau etena)
• Ada di alam cukup banyak
19
alkena di alam
• etilen �� gas yang berperan dalam proses
kematangan buah
• α-pinena �� komponen utama terpentin
• β-karoten �� pigmen oranye pemberi
warna wortel, sumber vit A dan memberi
perlindungan terhadap penyakit kanker
α-pinena
β-karoten
etilen
Tata nama
• nama senyawa menunjukkan posisi ikatan rangkaap Clk=Cena
• nama senyawa induk/utama berakhiran dengan –ena
• nama senyawa induk/utama ditentukan berdasarkan rantai C terpanjang
• angka pada nama alkena menyatakan atom C bernomer paling rendah
pada rantai yang mengandung ikatan rangkap C=C
• nama harus menyatakan isomer geometriknya jika ada
• penamaan sikloalkena mengikuti alkena dengan penomeran atom C
sedemikian rupa sehingga ikatan rangkap terletak diantara C1 dan C2,
dan gugus fungsi/substituen pertama berada pada posisi nomer C paling
kecil
C=C
C-CH2-CH3
CH3
H
CH3
H
C=C
H
CH3
C-CH2-CH3
CH3
H
4-metil-cis-2-heksena 4-metil-trans-2-heksena 1-metil-sikloheksena
1,5-dimetil-siklopentena
1,4-sikloheksadiena
20
Beberapa penamaan karena faktor sejarah, namun diterima oleh IUPAC:
• etena �� etilen
• lihat tabel
Reaksi pada alkena
• Preparasi alkena �� Cracking
– dekomposisi termal senyawa hidrokarbon rantai panjang menjadi
senyawa-senyawa yang lebih kecil (rantai pendek)
• Reaksi adisi (reaksi 2 senyawa untuk menghasilkan 1 produk
tunggal)
– hidrogenasi
– halogenasi
Preparasi alkena
• via termal cracking gas alam (alkana C1-
C4) dan gasolin rantai lurus (C4-C8)
21
Halogenasi dan hidrogenasi
• HALOGENASI �� aturan Markovnikov
C2H4 + HX �� CH3CH2X
C2H4 + X2 �� CH2X – CH2X
propilena + HBr �� 2-bromo propana dan atau 1-bromo propana
etilena + Br2 �� 1,2 dibromo etana
hidrogenasi
22
TINGKAT STABILITAS:
tetrasubstituted > tri-substituted > di- substituted > mono-substituted
isomer geometri alkenes
rotasimetil di sekitar C-C �� free, tidak
demikian dengan di sekitar C=C ��
sehingga struktur yang diperoleh tidak
bersifat mudah interkonversi tanpa
pemutusan ikatan
kemungkinan terbentuknya isomer
geometri
ikatan π putus sementara supaya
rotasi C-C dimungkinkan �� energi
barier ≥ energi ikatan π ~268 kJ/mol
NO
YES
23
stabilitas isomer geometri
alkena
• cis diklor etilen
• trans-diklor etilen
C=C
Cl
H
Cl
H
C=C
Cl
H
H
Cl
μ= 1,89 D
μ= 0 D
BP = 60,3 oC
BP = 47,5 oC
I. Aliphatic hydrocarbon –
alkynes
II. Aromatic hydrocarbon
24
Alkynes = Alkuna
• Hydrocarbons that contain a C-C triple bond
• Paling sederhana, asetilen H-C≡C-H
• The triple bond consists of an sp-sp s-bond and two pbonds.
• The remaining sp orbital on each carbon is oriented 180o
from the former sp orbital and forms a s-bond with another
atom.
Bonding
25
Reactions of alkynes
• Reduction to an alkene
– Geometrical isomerism possible for product, except
when alkyne is terminal (has triple bond at end).
Each of these
reactions is
stereoselective in
that each yields
predominantly
one stereoisomer
of two or more
possible ones.
• Reduction to an alkane
• Addition of Halogens
26
• Additions of Hydrogen Halides
Hydration of alkynes -
tautomerism
• Usually the equilibrium favors the ketone (or CH3 - CHO, when
the alkyne is acetylene) ��an acid - base equilibrium; -OH is a
stronger acid than -CH3.
• Structural isomers which exist in equilibrium with each other are
called tautomers.
• The particular type of tautomerism shown above is keto - enol
tautomerism.
27
Acidity of Alkynes – Alkynes in Synthesis —
• In general, it is possible to convert a terminal
alkyne to an anion by removing the terminal
hydrogen ��usually accomplished by using a base
which is stronger than an acetylide anion:
• The acetylide anion can be used in synthesis, to
make larger molecules, by reacting it with alkyl
halides in a substitution reaction:
• Example problem 1 –
• Synthesize 2-hexyne from starting materials
which do not contain more than 3 carbons.
28
Tatanama
• mengikuti aturan seperti pada alkana dan
alkena, akhiran –una
• posisi ikatan rangkap tiga dinyatakan oleh atom
C pertama di dekat ikatan
• penomeran atom C rantai utama sedemikian
rupa sehingga nomer C ikatan rangkap sekecil
mungkin
6-metil-3-oktuna
Tatanama
• Jika ada lebih dari 1 ikatan rangkap 3 �� diuna,
triuna, dst.
• Senyawa dengan 2 macam ikatan rangkap ��
enuna
– penomeran C dimulai dari ujung C plg dekat
sembarang ikatan rangkap; double bonds
nomernya lebih rendah drpd triple bonds
1-hepten-6-una
4-metil-7-nonen-1-una
29
Ring structures �� aromatic rings
• when carbons are arranged at the corners of a
hexagon with a hydrogen bonded to each carbon
and alternating double bonds between carbons
• the most basic ring structure is benzene (C6H6)
• H- substituted by functional groups �� variety
different molecules
• hydrocarbons based on the benzene ring �� arenes
– eg. benzene, toluene, naphtalene
• 1825, Michael Faraday isolated a new
hydrocarbon from illuminating gas, which he
called “bicarburet of hydrogen.”
• 1834, Eilhardt Mitscherlich of the University
of Berlin prepared the same substance by
heating benzoic acid with lime and found it to
be a hydrocarbon having the empirical
formula CnHn.
benzin
30
• Many trees exude resinous materials called balsams when
cuts are made in their bark �� some are fragrant – exotic oil
• Gum benzoin is a balsam obtained from a tree that grows in
Java and Sumatra.
• “Benzoin” is a word derived from the French equivalent,
benjoin, which in turn comes from the Arabic luban jawi,
meaning “incense from Java.”
• Benzoic acid is itself odorless but can easily be isolated from
gum benzoin.
• Compounds related to benzene were obtained from similar
plant extracts.
– tolu tree �� tolu balsam; 1840 found that distillation of tolu
balsam �� methyl derivative of benzene called toluene
Benzene
• Benzene is very unreactive
– • It gives substitution and not addition products
– only one monobromination product of benzene was ever
obtained �� all the hydrogen atoms of benzene are
equivalent.
• Substitution of one hydrogen by bromine gives the same product
as substitution of any of the other hydrogens.
– • It combines only with very reactive (usually
cationic) electrophiles
WHY ????
31
• 3 premises of August Kekulé (1866)
1. Benzene is C6H6.
2. All the hydrogens of benzene are
equivalent.
3. The structural theory requires that there be
four bonds to each carbon.
• Kekulé advanced: Four bonds to each carbon could be
accommodated by a system of alternating single & double
bonds with one hydrogen on each carbon.
• low reactivity of benzene and its derivatives reflects their
special stability.
• Kekulé was wrong: Benzene is not cyclohexatriene, nor is it
a pair of rapidly equilibrating cyclohexatriene isomers.
• 20 centuries later ��new electronic theory explaining the
stability of benzene’s ring
Teori Resonansi Struktur Bensena
• The two Kekulé structures for benzene have the
same arrangement of atoms, but differ in the
placement of electrons -- they are resonance forms,
and neither one by itself correctly describes the
bonding in the actual molecule.
• As a hybrid of the two Kekulé structures, benzene is
often represented by a hexagon containing an
inscribed circle – suggested firstly by Britain
chemist: Sir Robert Robinson �� aromatic sextet:
sextet”—the six delocalized electrons of the three
double bonds.
• Robinson’s symbol is a convenient time-saving
shorthand device, but Kekulé-type formulas are
better for chemical reaction
32
• Both Kekulé structures of benzene are of equal
energy, and one of the principles of resonance
theory is that stabilization is greatest when the
contributing structures are of similar energy.
• Cyclic conjugation in benzene, then, leads to a
greater stabilization than is observed in noncyclic
conjugated trienes.
• How much greater that stabilization is can be
estimated from heats of hydrogenation.
Hydrogenation of arenes in the presence of nickel requires high temperatures (100–
200°C) and pressures (100 atm).
1,3 sikloheksadiena
sikloheksena
33
Properties of Aromatic
Compounds —
• Cyclic and each atom in the
ring is a π-center (uses a p
atomic orbital to form π -type
bonds), ie, sp2 or sp.
• Ring is flat or nearly so
• High degree of unsaturation but
resistant to addition reactions –
generally undergo electrophilic
substitution (an electrophilic
reagent replaces a hydrogen
[usually] attached to the ring).
• Unusually stable.
• π -Electrons delocalized above
and below plane of ring.
aromatic heterocycles
kina – obat malaria
sulfapiridin – antibiotik
antipirin –
mengurangi
demam
1887
1938
1970s
1997
obat anti-ulcer
viagra– drug for
male impotence
treatment
34
• p409 Carey

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