CHM-134 Organic Chemistry Chapter 1 PDF

CHM-134 ORGANIC CHEMISTRY CHAPTER-1: BONDING & ISOMERISM 1.1 Introduction to Organic Chemistry I.2 Concepts of Bonding (Ionic-Covalent Bonding & Octet Rule) 1.3 Valence 1.4 The Shape of Molecules 1.5 Resonance 1.6 Orbitals 1.7 Oxidation State 1.8 Classification of Organic Compounds Accordi...

CHM-134 ORGANIC CHEMISTRY CHAPTER-1: BONDING & ISOMERISM 1.1 Introduction to Organic Chemistry I.2 Concepts of Bonding (Ionic-Covalent Bonding & Octet Rule) 1.3 Valence 1.4 The Shape of Molecules 1.5 Resonance 1.6 Orbitals 1.7 Oxidation State 1.8 Classification of Organic Compounds According to Functional Groups For more details please study: Organic Chemistry: Structure and Function Eighth Edition Asst. Prof. Gülbin KURTAY K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.1 INTRODUCTION TO ORGANIC CHEMISTRY In chemistry, organic and inorganic compound study is often divided. This is because reaction forms appear to be completely different between the two chemistry fields, and how they react. Indeed, they are so different that before the 1820s there was something fundamentally different between organic and inorganic compounds. They believed that only a «vital force» found in living creatures could make something organic. As Friedrich Wohler produced urea from non-organic compounds, the entire assumption was dissipated. Organic synthesis: Preparation complex organic chemicals from simpler, more readily available ones. Reactants (Substrates) = Starting compounds Products Reaction Mechanism = Underlying details of a reaction Reaction Intermediate = Chemical species formed and then destroyed on the pathway between reactants and products. For more details please study: Organic Chemistry: Structure and Function Eighth Edition Asst. Prof. Gülbin KURTAY K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.2 BONDING (IONIC AND COVALENT BONDING) Bonds are made by simultaneous coulombic attraction and electron exchange. Atom 1 + Atom 2 “favorable” A:A or A A  Opposite charges attract each other (Coulomb’s Law).  Electrons spread out in space (delocalization).  Noble gas configuration is desirable. For more details please study: Organic Chemistry: Structure and Function Eighth Edition Asst. Prof. Gülbin KURTAY K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.2 BONDING (IONIC AND COVALENT BONDING) This minimum energy is called the bond strength, and the distance between the two nuclei at this point is called the bond length. Bond strength For more details please study: Organic Chemistry: Structure and Function Eighth Edition Asst. Prof. Gülbin KURTAY K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.2 …IONIC BONDING Ionic Bonds are based on the transfer of one or more electrons from atom to another. The resulting cation and anion are electrosta attracted to each other. For more details please study: Organic Chemistry: Structure and Function Eighth Edition Asst. Prof. Gülbin KURTAY K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.2 …COVALENT BONDING Covalent Bonds are based on the sharing of electrons Dimensions: Nuclear diameter ~ 10-15 m five orders of Electronic orbit ~ 10-10 m magnitude Mass ratio proton ⁄ electron = ~ 1800 If the electrons are not shared equally, a polar covalent (partially ionic) bond is formed, otherwise a pure covalent bond is formed. For more details please study: Organic Chemistry: Structure and Function Eighth Edition Asst. Prof. Gülbin KURTAY K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.2 …THE OCTET RULE The periodic table underlies the octet rule. Electrons in atoms occupy levels or shells of fixed capacity. The first has room for 2, the second 8, and the third 16. Noble gases have 8 valence electrons (Helium: 2) and are particularly stable. Other elements lack octets in their outer electron shells and tend to form molecules in such a way as to create a stable octet arrangement. Duet Valence electrons Octets For more details please study: Organic Chemistry: Structure and Function Eighth Edition Asst. Prof. Gülbin KURTAY K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.2 …THE OCTET RULE In pure ionic bonds, electron octets are formed by transfer of electrons. Alkali metals react with halogens by the transfer of one electron from the alkali metal to the halogen. Both atoms achieve a noble gas configuration: the alkali metal that of the preceding inert gas, the halogen that of the following inert gas. IPNa = +119 kcal mol-1 EACl = -83 kcal mol-1 -LE = -120 kcal mol-1 ⊗E = -84 kcal mol-1 For more details please study: Organic Chemistry: Structure and Function Eighth Edition Asst. Prof. Gülbin KURTAY K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.3 VALENCE Valence electrons are conveniently indicated by placing dots around the symbol for an element. (The letters represent the nucleus and the core electrons, and the dots represent the valence electrons) Hydrogen can either lose an electron to form an H+ ion, or gain an electron to form a H-, or hydride, ion For more details please study: Organic Chemistry: Structure and Function Eighth Edition Asst. Prof. Gülbin KURTAY K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.3 VALENCE In covalent bonds, electrons are shared to achieve octet configurations  Ionic bonds between identical atoms of the same element do not form.  The high ionization potential of hydrogen prevents it from forming ionic bonds with halogens and other non-metallic elements.  Ionic bonds are also unfeasible for carbon since it would require the loss of 4 electrons to achieve the octet of the preceding inert gas, or the gain of 4 electrons to achieve the octet of the following inert gas. Shows only valence e- -4e +4e (He) C4+ C C4- (Ne)  In these and similar cases, covalent bonding occurs. Atoms share electrons to achieve a noble gas configuration. For more details please study: Organic Chemistry: Structure and Function Eighth Edition Asst. Prof. Gülbin KURTAY K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.3 VALENCE  In certain cases, one atoms supplies both of the electrons in the bond:  Often 4 electron (double) and 6 electron (triple) bonds are formed:  In most organic bonds, the electrons are not shared equally: polar covalent bonds.  Pure covalent bonds (perfect sharing of electrons) and ionic bonds (complete transfer of electrons) are two extreme types of bonding.  Most bonds lie somewhere between these extremes and are called polar covalent bonds.  Each element can be assigned an electronegativity value which represents its electron accepting ability when participating in a chemical bond. For more details please study: Organic Chemistry: Structure and Function Eighth Edition Asst. Prof. Gülbin KURTAY K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.4 VALENCE For more details please study: Organic Chemistry: Structure and Function Eighth Edition Asst. Prof. Gülbin KURTAY K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.4 THE SHAPE OF MOLECULES : : Diatomics: linear (of course), e.g. H : H Li : H : F : F : : : : : : Triatomics: either linear, e.g. : F : Be : F : not : F : Be F : : : or bent, when there are lone e-pairs, e.g. HO H Tetraatomics: either trigonal, e.g. Cl : : Cl : B or pyramidal, when there are Cl : lone e-pairs, e.g. N : H H H H Pentaatomics: tetrahedral, e.g. C H H H For more details please study: Organic Chemistry: Structure and Function Eighth Edition Asst. Prof. Gülbin KURTAY K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.5 RESONANCE Often several octet structures are possible for a molecule: Resonance forms A Molecule B.. −.. +.. O.. C O.. :O.. C O.... Octet Non-octet Form A Form B move electrons (pairs).. -.. - O :O: :O: C C C - - - - O O O O O O Carbonate, CO32- (All forms are equivalent) For more details please study: Organic Chemistry: Structure and Function Eighth Edition K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.6 ORBITALS The electron is described by wave equations.  An electron within an atom can have only certain definite energies called energy states.  Moving particles such as electrons exhibit a wavelength determined by the de Broglie relation:  Where h is Plank’s constant, m is the mass of the electron in kg, and v is the velocity of the electron in m/s. The electron waves contain nodes, where the amplitude of the wave changes sign, and can interact with each other, producing either constructive or destructive interference: For more details please study: Organic Chemistry: Structure and Function Eighth Edition K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.6.1 ATOMIC ORBITALS The simplest atomic orbitals are spherical in shape and are called s orbitals. The lowest energy s orbital is the 1s orbital. 1s 2s For more details please study: Organic Chemistry: Structure and Function Eighth Edition. K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.6.1 ATOMIC ORBITALS Of slightly higher energy than the 2s orbital are 3 degenerate 2p orbitals. These orbitals are shaped like a figure 8 and point along the 3 Cartesian axes. For more details please study: Organic Chemistry: Structure and Function Eighth Edition K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.6.2 MOLECULAR ORBITALS The bond in the hydrogen molecule is formed by the overlap of 1s atomic orbitals Atomic orbitals on different atoms may overlap. The overlap of electron waves represented by the atomic orbitals may result in constructive (in phase) or destructive (out of phase) interference. In phase overlap between two 1s orbitals results in a new orbital having lower energy than either of the s orbitals. This new orbital concentrates the electron probability between the two nuclei. Out of phase overlap between two 1s orbitals results in a new orbital having higher energy than either of the s orbitals. This new orbital places most of the electron probability to the left and right of the two nuclei. For more details please study: Organic Chemistry: Structure and Function Eighth Edition K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.6.2 MOLECULAR ORBITALS An energy level diagram can now be made of the two overlapping orbitals, and the Aufbau process used to determine the electronic configurations of H2 and He2: For more details please study: Organic Chemistry: Structure and Function Eighth Edition K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.6.3 HYBRID ORBITALS Mixing of atomic orbitals from the same atom results in new atomic orbitals of different energy and directionality. sp Hybrids produce linear structures: An incorrect structure for BeH2 is predicted if 2s and 2p orbitals of Be are overlapped with the 1s orbitals of H: For more details please study: Organic Chemistry: Structure and Function Eighth Edition K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.6.3 HYBRID ORBITALS Mixing the 2s orbital with one of the 2p orbitals of Be results in two new hybrid sp orbitals, each made up of 50% s and 50% p character. The resulting bond angle is 180o which corresponds with the observed bond angle in the BeH2 molecule Hybridization does not change the number of orbitals on the atom. In this case two atomic orbitals are replaced by two new hybrid orbitals. The two unhybridized p orbitals are still available to hold electrons. For more details please study: Organic Chemistry: Structure and Function Eighth Edition K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.6.3 HYBRID ORBITALS sp2 Hybrids create trigonal structures. Hybridization of a 2s and two 2p orbitals results in three new hybrid orbitals that point to the corners of an equilateral triangle. The remaining p orbital points up and down, perpendicular to each of the three hybrid orbitals. Bond angles in molecules using sp2 hybridization are approximately 120o For more details please study: Organic Chemistry: Structure and Function Eighth Edition K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.6.3 HYBRID ORBITALS sp3 hybridization explains the shape of tetrahedral carbon compounds. When the 2s and all three 2p orbitals are hybridized, four hybrid orbitals called sp3 orbitals are formed.These orbitals point to the corners of a regular tetrahedron. Bond angles in molecules using sp3 hybridization are approximately 109.5o For more details please study: Organic Chemistry: Structure and Function Eighth Edition K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.6.3 HYBRID ORBITALS Pi bonds are present in ethene (ethylene) and ethyne (acetylene). Molecules containing double or triple bonds contain unhybridized p orbitals that overlap lengthwise rather than end on. For more details please study: Organic Chemistry: Structure and Function Eighth Edition K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.7 OXIDATION STATE For more details please study: Organic Chemistry: Structure and Function Eighth Edition K. Peter C. Vollhardt (Author), Neil E. Schore (Author) ISBN-10: 1319079458 1.8 CLASSIFICATION OF ORGANIC COMPOUNDS ACCORDING TO FUNCTIONAL GROUPS Functional IUPAC Name Compound Prefix/Suffix Example Group (Common Name) Hydrocarbons R-H Alkane -ane CH3CH3 ethane C=C Alkene -ene H2C=CH2 ethene (ethylene) C≡C Alkyne -yne HC≡CH ethyne (acetylene) Ar-H Arenes -ene benzene Halogen-Containing Compounds R-X Haloalkane halo- CH3Cl chloromethane Ar-X Aryl halides halo- chlorobenzene Oxygen-Containing Compounds R-OH Alcohol -ol (hydroxy-) CH3OH methanol ArOH Phenols -ol phenol R-O-R Ether ether (alkoxy-) CH3OCH3 dimethyl ether RCOH Aldehyde -al CH3CHO ethanal (acetaldeyde) RCOR Ketone -one CH3COCH3 propanone (acetone) Carboxylic ethanoic acid (acetic RCOOH -oic acid CH3COOH acid acid) Carboxylic Acid Derivatives methyl ethanoate RCOOR Ester -oate CH3COOCH (methyl acetate) RCOOX Acyl halides -acyl CH3COOCl Acetyl chloride ethanamide RCONH2 Amide -amide CH3CONH2 (acetamide) RCOOCOR Anhydride -anhydride CH3COOOCH3 Acetic anhydride Nitrogen-Containing Acid Derivatives R-NH2 CH3CH2NH2 ethylamine Amine -amine (amino-) aminoethane RC≡N Nitriles -nitrile (cyano) CH3C≡N acetonitril For more details please study: Organic Chemistry: Structure and Nitro Function Eighth Edition K. Peter C. Vollhardt (Author), Neil E. ArNO2 -nitro nitrobenzene compounds Schore (Author) ISBN-10: 1319079458