Slide 4 Organic Chemistry Introduction

Kimia Organik 1. 2. 3. 4. 5.

Structure and Bonding review (11/11) Classes of Organic Compounds (11/11) Aliphatic Hydrocarbons (11/11) Aromatic Hydrocarbons (18/11) Chemistry of the Functional Groups (25/119/12): • • •

6.

Alcohol & Ethers Aldehyde & Ketones Carboxylic Acids & derivates

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

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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

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Classes of organic compounds Hydrocarbons

Aromatic

Aliphatic

Alkanes

Cycloalkanes

Alkenes

Alkynes

aliphatic hydrocarbons do not contain benzene group/ring aromatic hydrocarbons contain one or more benzene rings

Structure and Bonding review

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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.

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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.

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sp sp2 sp3

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 )

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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)

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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)

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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.

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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 Æ structural isomers n-butane and isobutane

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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 name

formula

Metana Etana Propana Butana Pentana Heksana Heptana Oktana Nonana Dekana

CH4 CH3 - CH3 CH3 – CH2 - CH3 CH3 – (CH2)2 - CH3 CH3 – CH2 - CH3 CH3 – CH2 - CH3 CH3 – CH2 - CH3 CH3 – CH2 - CH3 CH3 – CH2 - CH3 CH3 – CH2 - CH3

number of C 1 2 3 4 5 6 7 8 9 10

BP MP o (oC) ( C) -182,5 -161,6 -183,3 -88,6 -189,7 -42,1 -138,3 -0,5 -129,8 36,1 -95,3 68,7 -90,6 98,4 -56,8 125,7 -53,5 150,8 -29,7 174,0

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Alkane nomenclature based on recommendation of the International Union of Pure and Applied Chemistry (IUPAC)

1. 2. 3. 4. 5. 6. 7.

Nama utama berdasarkan rantai karbon terpanjang Rantai alkana kekurangan 1 atom H disebut gugus alkil, rantai cabang disebut gugus alkil Jika 1 atau lebih atom H diganti gugus lain, nama senyawa harus menunjukkan lokasi atom C tempat penggantian tersebut Pemberian nomer atom C rantai karbon terpanjang sedemikian rupa sehingga memberikan nomer lebih kecil untuk semua atom C bercabang Jika ada lebih dari 1 cabang alkil yang sama digunakan awalan di-, tri-,tetra-, … mengikuti nama alkil. Jika ada 2 cabang alkil berbeda, diberi nama sesuai gugus alkil diawali dengan nomer atom C posisi cabang tersebut Penamaan dengan cabang unsur mengikuti aturan nomer 6

Common alkyl groups Nama

Rumus

Metil

- CH3

Etil

- CH2 - CH3

n-propil

- CH2 - CH2 - CH3

- CH2 – CH2 - CH2 - CH3 n-butil CH3 Isopropil -C-H

t-butil

CH3 - C – CH3 CH3

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Functional groups Gugus fungsional

Nama

- NH2

Amino

-F

Fluoro

-Cl

Kloro

-Br

Bromo

-I

Iodo

- NO2

Nitro

- CH = CH2

Vinil

Beri nama senyawa berikut sesuai IUPAC CH3

CH3

CH3 – C – CH2 – CH – CH2 – CH3 CH3

Gambarkan struktur senyawa 2,2dimetil-3-etilpentana

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Aliphatic hydrocarbon • alkanes • cycloalkanes • alkenes • alkynes

Struktur proyeksi Newman proyeksi Sawhorse

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Reaksi kimia alkana • Pembakaran 0 – sangat eksotermis CH 4( g ) + 2O2( g ) → CO2( g ) + 2 H 2 O(l ) ∆H = −890,4kJ

2C 2 H 6 ( g ) + 7O2 ( g ) → 4CO2( g ) + 6 H 2 O(l ) ∆H 0 = −3119kJ

• Halogenasi alkana Æ alkil halida – substitusi 1 atau lebih atom H oleh atom halogen

panas RH + X 2 ⎯UV ⎯/⎯ ⎯→ RX + HX

CH 4 ( g ) + Cl 2 ( g ) → CH 3 Cl ( g ) + HCl ( g ) metil klorida

Jika tersedia gas klor berlebih:

• campuran gas metana CH 3Cl ( g ) + Cl 2( g ) → CH 2 Cl 2 (l ) + HCl ( g ) dan klor dipanaskan di metilen klorida atas 100 oC atau diiradiasi CH Cl + Cl 2 2(g) 2 ( g ) → CH Cl 3 ( l ) + HCl ( g ) cahaya dengan λ tertentu kloroform

Apakah nama sistematik (sesuai aturan penamaan) untuk metil klorida, metilen klorida dan kloroform?

Alkil halida • Kloroform – cairan volatil untuk anastesi – toksik thd ginjal, hati dan jantung Æ dilarang

• Karbon tetraklorida – cairan pembersih Æ noda minyak pada kain – toksik

• Metilen klorida – solven untuk de-kafeinasi kopi dan pembersih cat

• Klorofluoro karbon

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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

cortisone (a steroid) chrysanthemic acid penarik serangga

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 Æ C5 dan C6 banyak ditemui secara natural

C5 C6

C8

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Penamaan sikloalkana

metil siklopentana

1 siklo propil butana

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Penamaan sikloalkana

NOT

1,3 dimetil sikloheksana

1,5 dimetil sikloheksana

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

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alkena di alam • etilen Æ gas yang berperan dalam proses kematangan buah • α-pinena Æ komponen utama terpentin • β-karoten Æ 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 rangkap C=C alkena 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 1,4-sikloheksadiena

CH3 CH3

H H

4-metil-cis-2-heksena

H

1,5-dimetil-siklopentena

C=C

C-CH2-CH3

C=C H

CH3

C-CH2-CH3 CH3

4-metil-trans-2-heksena

1-metil-sikloheksena

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Beberapa penamaan karena faktor sejarah, namun diterima oleh IUPAC: • etena Æ etilen • lihat tabel

Reaksi pada alkena • Preparasi alkena Æ 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 C1C4) dan gasolin rantai lurus (C4-C8)

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Halogenasi dan hidrogenasi • HALOGENASI Æ aturan Markovnikov C2H4 + HX Æ CH3CH2X

etilena + Br2 Æ 1,2 dibromo etana

C2H4 + X2 Æ CH2X – CH2X

propilena + HBr Æ 2-bromo propana dan atau 1-bromo propana

hidrogenasi

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TINGKAT STABILITAS: tetrasubstituted > tri-substituted > di- substituted > mono-substituted

isomer geometri alkenes rotasi metil di sekitar C-C Æ free, tidak demikian dengan di sekitar C=C Î sehingga struktur yang diperoleh tidak bersifat mudah interkonversi tanpa pemutusan ikatan kemungkinan terbentuknya isomer geometri

NO

ikatan π putus sementara supaya rotasi C-C dimungkinkan Æ energi barier ≥ energi ikatan π ~268 kJ/mol

YES

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stabilitas isomer geometri alkena Cl Cl • cis diklor etilen

µ= 1,89 D

C=C H

H Cl

H C=C

• trans-diklor etilen

H

Cl

BP = 60,3 oC µ= 0 D BP = 47,5 oC

I. Aliphatic hydrocarbon – alkynes II. Aromatic hydrocarbon

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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

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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

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• Additions of Hydrogen Halides

Hydration of alkynes tautomerism

• Usually the equilibrium favors the ketone (or CH3 - CHO, when the alkyne is acetylene) Æan 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.

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Acidity of Alkynes – Alkynes in Synthesis — • In general, it is possible to convert a terminal alkyne to an anion by removing the terminal hydrogen Æusually 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.

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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 Æ diuna, triuna, dst. • Senyawa dengan 2 macam ikatan rangkap Æ enuna – penomeran C dimulai dari ujung C plg dekat sembarang ikatan rangkap; double bonds nomernya lebih rendah drpd triple bonds

4-metil-7-nonen-1-una 1-hepten-6-una

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Ring structures Æ 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 Æ variety different molecules • hydrocarbons based on the benzene ring Æ 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

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• Many trees exude resinous materials called balsams when cuts are made in their bark Æ 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 Æ tolu balsam; 1840 found that distillation of tolu balsam Æ 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 Æ 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 ????

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• 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 Ænew 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 Æ 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

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• 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

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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 1997

1938 1887

antipirin – mengurangi demam

sulfapiridin – antibiotik 1970s viagra– drug for male impotence treatment

obat anti-ulcer

kina – obat malaria

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• p409 Carey

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