VIETNAM NATIONAL UNIVERSITY OF AGRICULTURE ORGANIC CHEMISTRY Nguyễn Thị Hiển Department of chemistry Faculty of Environment science Vietnam national university of Agriculture 1 CHAPTER 1: GENERAL OF ORGANIC CHEMISTRY CONTENTS OF CHAPTER 1 1.1 The development of Organic Chemistry 1.2 The characteristics of the Carbon atom 1.3 Chemical bonding in organic chemistry 1.5 Classification of organic compounds 1.6 Classification of organic reactions 1.7 Isomerism in organic chemistry 2 New words Hybridization (N) Hybrid (adj) Configuration Conformation Contitutional isomers – Structural isomers Geometric isomers Optical isomers Enantiomers Diastereomers Primary – Secondary – Tertiary – Quaternary bond - link - connection 3 1.1 The development of Organic Chemistry Every living organism is made of organic chemicals: food you eat, medicine you take, wood, paper, plastics and fibers all organic chemicals that made modern life possible ……………………. ⚫ The term “organic chemistry” means the chemistry of compounds from living organisms. ⚫ In the past, the difference between organic and inorganic compounds is “vital force” organic compounds contained an undefinable “vital force” which was necessary for the synthesis of an organic compound. Friedrich WÖhler (1828) : From the pyrolysis of an inorganic compound, NH4OCN, synthesized urea (found in urine): NH4-OCN → H2N-CO-NH2 4 Source of Organic compounds ⚫ Organic compounds are derived from living organisms synthesized in the laboratory.
Medicines, dyes, polymers, plastics, pesticides, and a host of other organic substances,… are all prepared in the laboratory. Carbon is present in all organic compounds Organic chemistry is studying of carbon compounds (except CO, CO2, M2(CO3)n, M(HCO3)n) 5 1.2 The characteristics of the carbon atom * Carbon atoms can be linked with other carbon atoms to form: linear and branched chains, ring structures single, double or triple bonds. Carbon atoms can link with other elements such as hydrogen, oxygen, nitrogen, sulphur, halogen. Forming stable bonds The number of carbon compounds is very large.2 The characteristics of the carbon atom * The valence of carbon atom in organic compounds is IV C6 1s22s22p2 in the basic state 1s2 2s2 2p2 The attractive state Each carbon atom has 4 bonds with other atoms.
Ex: CH3-CH=CH2; C 2H 2; CH3COOH 7 THE VALENCE OF ELEMENTS IN ORGANIC CHEMISTRY Valence 1 4 3 2 8 1.2 The characteristics of the carbon atom * Hybridization of carbon atom sp3 hybridization sp3 Orbitals in the structure of Methane How does bonding in organic molecules with tetravalent carbon atoms occur? C6 1s22s22p2 The basic state 1s2 2s2 2p2 The attractive state 1s2 2s1 2p3 sp3 hybridization 9 * Hybridization of carbon atom sp3 hybridization 10 Methane molecule When the 4 identical sp3 orbitals of carbon overlap with the 1s orbitals of 4 H atoms, 4 identical C-H σ bonds are formed and methane results. Drawing tetrahedral angles of methane: The wedge is coming out of the paper and the dashed line is going behind the paper. The solid lines are in the plane of the paper. 11 A space-filling model of methane would look like.
Each C-H bond in methane has a 438 kJ/mol and a length of 110 pm. The bond angle formed by each H-C-H is 109.5o, the so-called tetrahedral angle. 12 * Hybridization of carbon atom sp2 hybridization the two 2p orbitals of the carbon atom are combined with its 2s orbital to form three new orbitals "sp2" hybrid orbitals. one unpaired electron in a non-hybridized p orbital.
13 * Hybridization of carbon atom sp2 hybridization Ex ethene molecule: In ethene, H2C=CH2 both C are sp2 hybridized. 4 C-H σ bonds are made by the interaction of Csp2 with 1s orbitals of H. 1 C-C σ bond is made by the interaction of Csp2 with another Csp2 orbital. 1 C-C bond is made by the interaction of the Cp with the other Cp orbital.
The 3-dimensional model of ethene is: planar with H-C-H and H-C-C bond angles of 120o. The pi-bond is not shown in this picture. 14 * Hybridization of carbon atom sp hybridization In the molecule Acetylene (C2H2), both carbon atoms will be sp hybridized and have one electron in each of two unhybridized p orbitals. 15 * Hybridization of carbon atom sp hybridization Ex: axetylene molecule Both C are sp hybridized 2 C-H σ bonds are made by the interaction of C sp with H1s orbitals (see red arrows) 1 C-C σ bond is made by the interaction of C sp with another C sp orbital (green arrow) 2 C-C bonds are made by the interaction of the 2 pairs of C p orbitals (black arrows) The 3-dimensional model of acetylene is: therefore linear.1 Draw a line-bond structure for propene, CH3CH=CH2; indicate the hybridization of each carbon and predict the value of each bond angle.2 Draw a line-bond structure for 1,3-butadiene, H2C=CH-CH=CH2; indicate the hybridization of each carbon and predict the value of each bond angle.
17 * Primary, secondary, tertiary and quaternary nomenclature (Levels of carbon atoms) Carbon atoms have 4 levels: + Primary: bonded to another carbon atom with a single 1 2 3 4 5 bond. (1O) CH3-CH=C-CH2-CH3 + Secondary: bonded to 2 carbon atoms with 2 single CH3 bonds or 1 carbon atom with a double bond.1;5; or 1 triple bond or 1 double bond and 1 single bond.4) + Quaternary: Carbon atoms bonded to other carbon atoms with 4 bonds.3) Convention : the level of a C atom in compounds with only 1C is primary. C of functional groups 19 1.3 Chemical bonding in organic chemistry The octet rule: atoms will be stable with 8 electrons in the valence shell like noble gases. Covalent Bonds ⚫ When two or more atoms of the same or similar electronegative or close electronegative react to form bonds, a complete transfer of electrons does not occur.
In this case, the atoms achieve noble gas configuration by sharing electrons. The covalent bonds formed between these atoms by sharing their electrons. 20 Valence Bond Theory Valence bond theory describes a chemical bond as the overlap of atomic orbitals. Ex 1: The hydrogen molecule: the 1s orbital of one hydrogen atom overlaps with the 1s orbital of the second hydrogen atom to form a molecular orbital called a sigma bond, σ.
H↑ + ↓H → H↑↓ H Ex 2: The methane molecule: CH4 the 1s orbital of each hydrogen atom overlaps with 1sp3 hybrid orbital of the carbon atom to form a molecular orbital called a sigma bond, σ. 21 Characteristics of covalent bonds There are 2 kinds of covalent bonds: sigma bond and pi bond. The bond axis is the line conecting 2 atomic nuclei. • Sigma bond (): formed by the axis overlap of hybrid obitals together; hybrid obitals with AOs or AOp; AOs together; AOp together or AOs with AOp.
+ (a): sigma bond: A hybrid obital overlaps with an AOs. + (b): sigma bond: Two hybrid obitals overlap together + (c): pi bond: Two AOp overlap together. Characteristics of covalent bonds • Sigma bond (): + axis overlap + stable + single bonds are sigma bonds. • Pi bonds () : + boundary overlap + unstable + pi bonds create multiple bonds a double bond: a sigma bond and a pi bond a triple bond: a sigma bond and two pi bonds.
The organic compounds containing pi bonds are more active than those only sigma bonds. Characteristics of covalent bonds • Bond energy: the energy makes the bond broken. Question: compare the durability of the link: single, double, triple carbon-carbon. • Bond length: an optimum distance between nuclei that leads to maximum bond stability, a distance called the bond length.
The bond energy is larger, the bond length is shorten. • Bond polarity: the bond X-Y called: + a non-polar covalent bond when 0 |X-Y| 0,4 + a polar covalent bond when 0,4 < |X-Y| 1,7 (X; Y are the electronegativity of X and Y). The polarity of bonds: in a bond, the atom with larger electronegativity attracts electrons toward it.5 Ex: liên kết C-H, C-C : non-polar O: 3.5 liên kết C-O, O-H : polar : 2.4 Inductive effect ⚫ When speaking of an atom’s ability to polarize a bond, we often use the term inductive effect. ⚫ The carbon-carbon bond of ethane is completely nonpolar at each end of the bond there are two equivalent metyl groups: CH3 – CH3 But CH3-CH2-F 27 ⚫ This is not the case with the carbon-carbon bond of Ethyl fluoride: + + - CH3 CH2 F One end of the bond, the one nearer the fluorine atom, is more positive than the other.
This polarization of the C-C bond results from an intrinsic electron-attracting ability of the fluorine (because of electronegativity) that is transmitted through space and through the single bonds of the molecule. 28 ⚫ Chemists call this shifting of electrons an inductive effect, denoted I. The inductive effect here is electron attracting (or electron withdrawing), denoted –I Ex: -NO2; F; Cl, Br; I; -SO3H; -CN; -OH, -NH2, -CHO, -COOH, groups with multiple bonds The group's electronegativity is larger, the electron attracting ability is stronger. Ex : -F > -Cl > -Br > -I ⚫ The saturated hydrocarbon radicals donate electrons (or electron releasing), denoted +I.
The saturated hydrocarbon radicals are larger, more cumbersome; the electron releasing ability is stronger. Ex: t-C4H9 > iso-C3H7 > -C3H7 > -C2H5 > -CH3 29 Characteristics of Inductive effect - The inductive effects weaken as the distance from the substituent increase. ⚫ in this case, the positive charge that the fluorine imparts to C1 is greater than that imparted to C2 because the fluorine is closer to C1. - The inductive effect only transmits through the single bond chain of molecules.4 Compare the polarity of C-Cl bonds in these compounds: CH3Cl; C2H5Cl; CH3CH(CH3)Cl; 1.5 Compare the acidity of these acids: HCOOH; CH3COOH; ClCH2COOH; Cl3CCOOH 31 Practice problem KEY 1.4 The polarity of C-Cl bonds in these compounds increases as follows: CH3-Cl < C2H5-Cl < CH3CH(CH3)Cl Because alkyl radicals make +I and +I: CH3- < C2H5- < i-C3H7- 1.5 The acidity of these acids increases as follows: CH3COOH < HCOOH < ClCH2COOH < Cl3CCOOH +I (CH3) 0 -I(Cl) -I(3 Cl) 32 1.5 Classification of organic compounds ⚫ More than 22 mill.
organic compounds, each has its own unique physical and chemical properties. ⚫ The organic compounds are classified into families according to their structural features based on (i)- the carbon skeleton and (ii)- the functional groups. 33 The carbon skeleton a. Acyclic or open chain compounds: alkanes, alkenes, alkynes and their derivatives.
They are also called aliphatic compounds b. Cyclic or closed chain compounds: Rings are made up of only one kind atoms, (carbon atoms) are called homocyclic or cabocyclic compounds. 34 ⚫ Aliphatic cyclic compounds are called alicyclic compounds e.g cyclopropane, cyclobutane : cyclohexane : 35 Organic compounds containing one or more fused or isolated benzene rings and their functinalized derivatives are called benzenoids or aromatic compounds, eg benzene, toluene, naphthalene, anthracene etc. 36 Cyclic compounds containing one or more heteroatoms (usually O, N, S etc) are called heterocyclic compounds eg ethylene oxide, tetrahydrofuran (THF), furan, pyrole etc.
O O Ethylen oxide tetrahydrofuran (THF) 37 Functional groups ⚫ It is possible to classify organic compounds by their reactivity, e.g by so-called functional groups. ⚫ According to the functional groups organic compounds can be divided into: ⚫ alkanes, alkenes, alkynes, arenes, halides, alcohols, etc. 38 The functional groups. ⚫ A functional groups is an atom or a group of atoms within a larger molecule that has a characteristic chemical behaviour.
⚫ Chemically, a given functional group behaves almost the same way in every molecule it’s in.