Basic Principle of Organic Chemistry Lecture Notes PDF

Dr. Ghada Emad Basic Principle of Organic CHEMISTRY Chem 101 Dr. Ghada Emad  Organic Chemistry Organic Chemistry is the study of the structure, properties, composition, reactions, and preparation of carbon-containing compounds, exactly, compoun...

Dr. Ghada Emad Basic Principle of Organic CHEMISTRY Chem 101 Dr. Ghada Emad  Organic Chemistry Organic Chemistry is the study of the structure, properties, composition, reactions, and preparation of carbon-containing compounds, exactly, compounds containing Carbon-Hydrogen bonds, which distinguish them from inorganic chemistry. Organic compounds form the basis of all earthly life and consider the central substances of which all-living things on our planet are made. Proteins, Enzymes, lipids, Fats, Nucleic acids, Vitamins, Hormones, Carbohydrates and others are all naturally occurring organic compounds Dr. Ghada Emad  Empirical formula Chemical formula Structural formula Molecular formula Dr. Ghada Emad 1- Empirical Formula The empirical formula is the simplest whole-number ratio of the atoms in a compound. Examples: Benzene CH Glucose CH2O C4H8 CH2 Factor =4 Dr. Ghada Emad B2H6 BH3 Factor =2 2- Molecular Formula The molecular formula is the actual number of the toms of a compound. Examples : benzene C 6H 6 Glucose C6H12O6 CH2 C4H8 Factor =4 BH3 B2H6 Factor =2 Dr. Ghada Emad Dr. Ghada Emad Molecular Formula Empirical Formula Factor =6 Factor =2 Factor =2 Factor =2 Factor =2 Factor =6 Factor =2 Factor =2 Factor =5 Dr. Ghada Emad  Calculating Empirical Formulas for Compounds  Calculating Molecular Formulas for Compounds Dr. Ghada Emad  Calculating Molecular Formulas for Compounds Molecular formulas give the kind and number of atoms of each element present in the molecular compound the empirical formula of a compound of boron and hydrogen is BH3. Its molecular formula molar mass is 27.7g/mol. Determine the molecular formula of the compound. Knowing that the mass number of H=1, B=10 Dr. Ghada Emad  How to calculate the Empirical formula The percent composition of a compound was found to be 63.5 % Silver, 8.2 % Nitrogen and 28.3 %Oxygen. Determine the Empirical formula of this compound ( Knowing that the mass number of Ag =107.87 , N=14, O= 16 Atoms Ag N O Mass 63.5 8.2 28.3 63.5 8.2 mass Mole = 0.585 28.3 = 1.769 Mole = 107.87 14 =0.585 16 Molar mass 0.585 0.585 Mole ratio 1.769 =1 0.585 = 1 =3 0.585 0.585 AgNO3 Empirical formula Dr. Ghada Emad  How to calculate the Empirical & Molecular formulas Find the Empirical & molecular formulas of a compound contains 38.7 g carbon , 9.62 g Hydrogen and 51.6 g Oxygen. Its molar mass is 62 g. ( Knowing that the mass number of C=12, H=1 , O=16 Atoms C O H Mass 38.7 51.6 9.62 Mole 38.7 51.6 9.62 12 = 3.22 =3.22 = 9.62 16 1 Mole ratio =1 = 1 =3 Empirical formula CH3O Empirical formula mass = (1x12) + (1x3) + ( 1x16) = 31.03 62 = 2 Molecular formula C2H6O2 31.03 Dr. Ghada Emad  Problem1 The empirical formula of hexane is C3H7. Its molecular weight is 86.2. What is the molecular formula of hexane? (Ans:C6H14) Problem 2 Calculate the empirical formula of a compound whose composition is 65.68% C, 15.16% H, and 19.16% N? (Ans: C4H11N) Problem 3 The empirical formula of a compound is CH2O. 0.0835 moles of the compound contains 1.0 g of hydrogen. Molecular formula of the compound is Dr. Ghada Emad 3- Structural Formula Show how atoms in the molecules connected and bonded to each others C2H6O Empirical formula of Molecular formula of Structure formula of ethane ethane ethane Dr. Ghada Emad   Representation the structural formulas Skeletal Lewis's structure Structure Structural Formula Condensed valence-bond Structure structure Dr. Ghada Emad  1. Lewis structure (electron dot formula structure) Each bond is represented as 2 dots (:), or a dash (-) Dr. Ghada Emad  valence-bond formula  Each bond is represented as a dash (-) Dr. Ghada Emad  Problem: Q: Write the valence-bond formula for each of the following Lewis formulas: Dr. Ghada Emad  3. Condensed Structure  Gives us the different groups in the molecule. Divided in two types  In Partially condensed structure: show the bonds between different groups) CH3 CH2 CH2 CH2 CH3  In fully condensed structure: all bonds disappear CH3 (CH2)3 CH3 Dr. Ghada Emad Dr. Ghada Emad  4. Skeletal Structure  Line-angle structure or line bond structure  Rules for drawing skeletal structure: Rule 1: All carbon-carbon single bonds are shown as a single line Rule 2: Double bonds are shown as two parallel lines, Triple bonds are shown as three parallel lines. Rule 3: The chemical symbol of carbon, C, is omitted. A continuous carbon chain is represented as a zigzag arrangement of lines. Rule 4: Heteroatoms are atoms other than carbon or hydrogen and must be written. Rule 5: Hydrogen atoms must be drawn on heteroatoms and the carbons of aldehyde groups. Note: Since carbon atoms ALWAYS have 4 bonds, you can determine the number of H atoms bonded to a particular carbon atom by counting the number of bonds and subtracting this value from 4. Dr. Ghada Emad Dr. Ghada Emad  3-Dimensional arrangement)  It is very helpful to use the 3-dimentional molecular models to visualize the relative positions of the atoms in space.  a) perspective drawing: Dr. Ghada Emad   B) Ball-and-stick model:  Use balls or spheres to represent the atoms and sticks to represent the bond between them.  Shows the relative size between atoms  B) Space-filling model:  Use interconnected spheres to show the electron clouds of atoms connecting together. Dr. Ghada Emad Dr. Ghada Emad   Cyclic compounds and polygon formulas Cyclic structures are usually represented by polygon formulas  What about shapes of cyclic compound Dr. Ghada Emad Dr. Ghada Emad Structural Classification of Carbon and Hydrogen Atoms Classification of Carbon Atoms:  A primary carbon atom (1o) is attached to only one other carbon atom.  A secondary carbon atom (2o) is attached to two other carbon atoms.  A tertiary carbon atom (3o) is attached to three other carbon atoms.  A quaternary carbon atom (4o) is attached to four other carbon atoms. Dr. Ghada Emad  Classification of Hydrogen Atoms Each Hydrogen atom is similarly classified and being given the same designation of 1o, 2o and 3o according to the carbon atom to which it is attached 1 3 1 1 2 2 1 H H H H H H H H C C C H H C C C C H H 2 H H C H H H H H H Dr. Ghada Emad  Octet Rule  A bond results from the attraction of nuclei for electrons  All atoms trying to achieve a stable octet  Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons makes an atom very stable Dr. Ghada Emad  Orbital Theory and hybridization Atoms are made of subatomic particles: protons, neutrons, & electrons Dr. Ghada Emad Dr. Ghada Emad  Electronegativity Electronegativity : is a measure of the ability of an atom to attract a bonding pair of electrons. Fluorine (the most electronegative element) is assigned a value of 4.0.  Elements with a HIGH electronegativity have a STRONG pull on electrons.  Elements with a LOW electronegativity have a WEAK pull on electrons. Dr. Ghada Emad Electronegativity decrease Electronegativity increase Dr. Ghada Emad  When two atoms bond their DIFFERENCE in Gain electrons Loss electron electronegativity determines the bond type Share electron Two Major Types of Bonding 1- Ionic Bonding which is formed when two atoms of widely differing electronegativity 2-Covalent Bonding which is formed Between nonmetallic elements of similar electronegativity pairs of (e-) are shared between non-metal atoms Dr. Ghada Emad  Ionic Bond is formed between two atoms have large difference in electronegativity. ( EN more than 1.7). which is formed by the transfer of one or more electrons from one atom to another ionic compounds are made of ions. ionic compounds are called Salts or Crystals Dr. Ghada Emad Dr. Ghada Emad Dr. Ghada Emad  Covalent bond  Between nonmetallic elements of similar electronegativity  Formed by sharing electron pairs between non- metal atoms  there are two types of covalent bond:  Non polar covalent bond:  when electrons are shared equally (EN less than 0.5) as H2 ,O2,Cl2 Cl2 Dr. Ghada Emad  A polar covalent bond:  when electrons are shared between different atom as H2O and CO2 When the electronegativity of two bonding atoms is much higher and the atoms don’t pull equally (EN 0.5-1.7). + - - + - H3C NH2 + O + H3C O H H H Dr. Ghada Emad  IONIC COVALENT Transfer electrons Share electrons Between an atom of high electronegativity and an Between two atoms of atom of low equal or very close electronegativity electronegativities NaCl N2 SO….. Ionic and covalent bonds are very different, but how do we predict if a bond will be ionic or covalent? Dr. Ghada Emad Dr. Ghada Emad  Orbitals theory and hybridization Atomic Orbitals  Electrons reside in general regions of space around the nucleus called shells.  Electrons restricted to specific regions of space called Atomic orbitals  There are four different kinds of orbitals for electrons s, p, d, and f.  The first shell, it is closest to the nucleus and is the smallest of the shells contain one orbital called the 1s orbital(spherical shape).  The second energy level contain one (s) orbital called 2s and three (p) (Px, Py, Pz) orbital called 2p orbitals (dumbbell shape).  The third energy level contain one (s) orbital called 3s , three (p) (Px, Py, Pz) orbital called 2p orbitals and five 3 (d) orbitals (dumbbell shape). Dr. Ghada Emad  The s-orbital, which is spherical, is do not have more than two electrons  p-orbital, which is pairs of dumbbells, aligned along x, y and z-axis at 90° to each other  d-orbital, have complex shape, f-orbital: have very complex shape. Dr. Ghada Emad  C 6 : 1s22s22p2 Dr. Ghada Emad Dr. Ghada Emad  Hybridization Hybridization is the mixing of atomic orbitals to form new orbitals with different energies and shapes than the original orbitals Hybridization is the combining of different types of orbitals The hybridization of different types of orbitals allows the atom to form more bonds and bonds that are equal. This results in a more stable molecule. 1-sp3-hybridization or Tetrahedral (1s+ 3p) 2- sp2-hybridization or Trigonal (1s+ 2p) 3- sp-hybridization or Diagonal (1s+ 1p) In this process, the new orbitals come into existence and named as the hybrid orbitals. Dr. Ghada Emad 1) sp3 – Hybridization  It occurs when one s-combine with three p-orbitals to form four equivalent  unsymmetrical tetrahedral orbitals (S + 3P = SP3).  having a tetrahedral structure  bond angle 109.5 degrees  Ex: CH4 , H2O , NH3, BeCl2 Dr. Ghada Emad The sp3 hybrid orbitals in CH4 H H sp3 σ 109.5° sp3 σ σ sp3 Hsp3 H H sp3 sp3 sp3 σ sp3 H H 109.5° H Dr. Ghada Emad  Types of Covalent Bonds A sigma (σ) bond is formed by end-to-end overlap of orbitals. All single bonds are σ bonds. Dr. Ghada Emad The sp3 hybrid orbitals in NH3 Dr. Ghada Emad  O6 12 The sp3 hybrid orbitals in H2O Dr. Ghada Emad  2) sp2 – Hybridization  Hybridization one s- and two p-orbitals are mixed form three sp2– hybrid orbitals.  having a planar triangular structure  Bond angle 120 degrees.  Ex: C2H2, BF3 Dr. Ghada Emad The sp2 hybrid orbitals in C2H4 CH2=CH2 Ethene Dr. Ghada Emad  A pi (p) bond is formed by sideways overlap of orbitals. A p bond is weaker than a σ bond because sideways overlap is less effective than end-to-end overlap. A double bond consists of one σ bond and one p bond Dr. Ghada Emad  3) SP – Hybridization  hybridization one s- and one p- orbital are mixed to form two sp – hybrid orbitals,  having a linear structure  Bond angle 180 degrees Dr. Ghada Emad The sp hybrid orbitals in C2H2 Dr. Ghada Emad Dr. Ghada Emad Hybridization NO. of σ bonds NO. of π Shape bonds SP3 S+ 3P Single bond 4 0 tetrahedral SP2 S+ 2P Double 3 1 planar bond triangular SP S+P Trible bond 2 2 Linear Dr. Ghada Emad  Examples : Dr. Ghada Emad