KIMIA DASAR I

APAKAH KIMIA ORGANIK ? Ilmu yang mempelajari senyawa-senyawa hidrokarbon dan derivatnya Perbandingan : 7 million senyawa organik 1.5 million senyawa anorganik

SENYAWA ORGANIK Materi tanaman / hewan Makanan Bahan farmasi/ kosmetik Plastik Komponen minyak bumi Pakaian

Some organic chemicals DNA Essential oils Medicines Active Pharmaceutical Ingredients Excipients Materials Fuels Pigments

alkana, alkena, alkuna, benzena Berdasarkan ikatannya Hidrokarbon jenuhHidrokarbon tak jenuh H I D R O K A R B O N Senyawa yang terdiri dari karbon dan hidrogen

Unsur kehidupan di atas bumi adalah C MENGAPA ??? memiliki 4 buah elektron bonding yang dapat membentuk ikatan kovalen yang kuat, dapat berupa ikatan tunggal dan rangkap (2 atau 3) Carbon (C)

Molekul organik paling sederhana: Covalent Bonding – Atoms Share Electrons Susunan OKTET yang stabil metana

ALKANA

Bentuk dasar Hibridisasi Bentuk tereksitasi 4 sp 3

Struktur tetrahedral pada metana Carbon yang menunjukkan hibridisasi sp3 4 buah ikatan C-H yang ekivalen (ikatan  ) Semua ikatan tunggal dinamakan ikatan 

Alkana C n H 2n+2 consist of only carbon and hydrogen bonded by single covalent bonds single Skeletal structure of only carbon atoms

Contoh : 2-metilbutana 4-etil-2-metilheksana = 6 3-etil-5-metilheksana3 + 5 = 8 

SIFAT FISIK Senyawa non polar, densitas <1, dengan air membentuk dua lapisan Larut dalam pelarut organik non polar Alkana C  4, berbentuk gas, Alkana Mr >, berbentuk cair, Alkana Mr >>>, berbentuk padat Semakin besar jumlah atom C, Mr molekul semakin >, gaya dispersi tiap molekul >, titik didih semakin tinggi Alkana bercabang td < alkana rantai lurus padanannya Ada pengaruh gaya van der Waals antar molekul Ikatan tunggal mampu berotasi bebas

Melting (blue) and boiling (pink) points of the first 14 n-alkanes in °C.

Isomers – the have the same molecular formula, but a different structures Structural Isomers – same molecular formula, but atoms are bonded in different orders. Has the same molecular formula as n-pentane, C 5 H 12 Has different Physical Properties : m.p, b.p. density C 4 H 10 – has two isomers, n-butane and isobutane (2-methylpropane) (2,2-dimethylpropane) (2-methylbutane)

CYCLOALKANES C n H 2n

Bond angles 60 ° Bond angles 88 ° Bond angles 108 ° Cyclohexane Bond angles ° Cyclopropane Cyclobutane Cyclopentane

1,2-dimetilsikloheksana tert-butilsiklopentana metilsikloheksana

How to draw Cyclohexane ? put in axial H’s put in equitorial H’s

REACTIONS OF ALKANES Combustion Dehydrogenation Halogenation – radical substitution reactions

Halogenation Substitution Reaction – a reaction in which part of a small reacting molecule replaces an atom or a group of atoms on the organic molecule

22 27/11/2015 Alkyl Halides or Haloalkanes

Naming them Tetrachloromethane or carbon tetrachloride 2-Chloro-3-methylbutane3-Bromo-1-chlorobutane 1-Ethyl-2-fluorocyclohexane 1-Bromobutane 2-Chloropropane or Isopropyl chloride Tend to be Heavier than water More Toxic than Alkanes Trichlorofluoromethane (Freon-11) Dichlorodifluoromethane (Freon-12) 1,1,1, 2-Tetrafluoroethane Chlorofluorocarbons (CFCs) Refrigerant Gases, Ozone Depletion, More H’s more degradable

 -- Nu - Electronegativity is defined as the ability of atoms to attract shared electrons in a covalennt bond leads to nucleophilic substitution in alkyl halides X is readily displaced by nucleophiles Symmetrical molecules have no dipole moment or have equal distribution of electrons within covalent bonds Therefore, they are unreactive!

25 27/11/2015 STEREOCHEMISTRY

Isomers are different compounds that have the same molecular formula Structural isomers are isomers that differ because their atoms are connected in a different order Stereoisomers differ only in the arrangement of their atoms in space Geometric Isomers CH 3 OCH dimethyl ether and CH 3 CH 2 OH ---- ethanol

Enantiomers are stereoisomers whose molecules are nonsuperimposable mirror images of one another Involves a tetrahedral sp 3 atom

One structure can be superimposed on another If any of the groups attached to the tetrahedral atom are the same, the centre is achiral. The ultimate way to test for molecular chirality is to construct models of the molecule and its mirror image and then determine whether they are superimposable Screwdriver is achiral Socks are achiral Golf club is chiral Gloves are chiral

Properties of Enantiomers Enantiomers have identical melting points and boiling points Enantiomers have identical solubilities in solvents Enantiomers have identical spectra and refractive index Enantiomers interact, and react with achiral molecules in the same manner Enantiomers interact and react with other chiral molecules at different rates Enantiomers rotate plane-polarised light by equal amounts but in opposite directions Polarimeter is a devise used to measure the effect of plane- polarised light on an optically active compound Chiral molecules are optically active

30 27/11/2015 No Correlation between the direction of rotation of plane polarised light and the absolute configuration of a molecule Clockwise Rotation (+) – dextrorotatory Anti-Clockwise Rotation (-) – levorotatory An equimolar mixture of two enantiomers is called a Racemic Mixture It is Optically Inactive

31 27/11/2015