New Mansoura University Organic Chemistry Lecture 1+2 PDF

New Mansoura University Faculty of Science Organic Chemistry CHE 111 Lecture 1+2 Prepared by: Dr. Eslam Abdelghaffar  Lecture Outlines. Definition Of Organic 1 Chemistry. 2 ATOMS, ELECTRONS, AND...

New Mansoura University Faculty of Science Organic Chemistry CHE 111 Lecture 1+2 Prepared by: Dr. Eslam Abdelghaffar  Lecture Outlines. Definition Of Organic 1 Chemistry. 2 ATOMS, ELECTRONS, AND ORBITALS Chemical bonds and 3 Chemical parameters Lewis structures, conformers 4 Classification of carbon atoms Conformers  Organic Chemistry: The chemistry of carbon and carbon- based compounds. (Carbon is the backbone of the of the life)  Organic compounds are compounds that contain carbon atoms. What makes carbon so special? Why are there so many carbon-containing compounds? 2 ATOMS, ELECTRONS, AND ORBITALS  Atom ic Structure: Orbitals Shapes o f A t o m i c Orbitals f o r Electrons ▪ Four different kinds of orbitals for electrons based on those derived for a hydrogen atom ▪ Denoted s, p, d, and f ▪ s and p orbitals most important in organic and biological chemistry ▪ s orbitals: spherical, nucleus at center ▪ p orbitals: dumbbell-shaped, nucleus at middle ▪ d orbitals: cloverleaf-shaped, nucleus at center  Filling Rules f o r Electron Orbitals Aufbau Principle: Electrons are added one at a time to the lowest energy orbitals available until all the electrons of the atom have been accounted for. Pauli Exclusion Principle: Each orbital is allowed a maximum of two electrons must spin in opposite directions. Hund’s Rule: Electrons first occupy each orbital singly with parallel spins before pairing  Energy Level Diagram o f a Many-Electron A to m 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p Valence Electrons: Valence electrons are electrons in the outermost shell. The most important electrons: because the electrons of this shell are the ones that an atom uses in making chemical bonds with other atoms to form compounds. Valence electrons is equal to the group number of the atom. For example, carbon is in group IVA and carbon has four valence electrons; oxygen is in group VIA and oxygen has six valence electrons. The halogens of group VIIA all have seven electrons.  Ans For practice: https://terpconnect.umd.edu/~wbreslyn/chemistry/electron-configurations/configurationPotassium.html  IONIC AND COVALENT BONDS Why atoms come together to form bonds? ❖An atom is most stable if its outer shell is either filled (contains eight electrons (octet rule) except 1s (2 e)) or empty. ❖ A hydrogen atom has one valence electron. Therefore, it can achieve a completely empty shell by losing an electron or a filled outer shell by gaining an electron. ❖ Lithium (Li) has a single electron in its 2 s orbital. If it loses this electron, the lithium atom ends up with a filled outer shell—a stable configuration. Lithium, therefore, loses an electron relatively easily ❖ Sodium (Na) has a single electron in its 3 s orbital, so it too loses an electron easily. ❖Fluorine has seven valence electrons Consequently, it readily acquires an electron in order to have an outer shell of eight electrons, thereby forming F-, a fluoride ion. F9 1s22s22p5 ❖Chlorine has seven valence electrons Consequently, it readily acquires an electron in order to have an outer shell of eight electrons, thereby forming Cl-, a chloride ion. Cl17 1s22s22p63s23p5  Chemical bonds Types of bonds. 1 Ionic bonds. 2 Covalent bonds.  Ionic bond ▪ Ionic bonds are formed between molecules or between ions with opposite charges. ▪ The negatively charged anion will electrostatically attract the positively charged cation. ▪ This is present in salts. ▪ Ionic compounds are formed when an element on the left side of the periodic table transfers one or more electrons to an element on the right side of the periodic table. ▪ A bond formed as a result of the electrostatic attraction between ions of opposite charge ▪ Are formed always between metal (lose electron) cations and non-metals anions (gain electron) so they exchange electrons to form the bond. ▪ Cation (+Ve charge) is formed when atom lose electron ▪ Anion ( -Ve charge is formed when atom gain electrons)  Properties o f Ionic Compounds Hard solid High mp temperatures Nonconductors of electricity in solid phase Good conductors in liquid phase or dissolved in water (aq)  ▪ Covalent bonds ▪ Formed when a pair of electrons is shared between two atoms. ▪ Covalent bonding like Ionic bonding results in a more stable compound, because the atoms involved meet the “octet rule”. ▪ Occurs between NON-METALS (ex. H, C, O, N…), which need to gain electrons to get a stable octet of electrons or a filled outer shell. ▪ The tendency for an atom to achieve a configuration where its valence shell contains eight electrons is called the octet rule Properties of Molecular Substances Low m.p. temp and b.p. temps Covalent bonding Relatively soft solids as compared to ionic compounds Poor conductors of electricity A “shared” pair of electrons makes a SINGLE BOND (2 total e-). 2 “shared” pairs makes a DOUBLE BOND (4 total e-). 3 “shared” pairs makes a TRIPLE BOND (6 total e-). C O V A L E N T BONDS and I O N I c bond ⚫ Unlike ionic bonds with transferred electrons, covalent bonds Sharing electrons. IONIC BOND COVALENT BOND  Electronegativity is the attraction an atom has for a shared pair of electrons.  Increases from left to right going across a period on the periodic table. Increases from the bottom to the top of the periodic table. (F > O > N, Cl > Br > I > S, C > H)  Electronegativity and Dipole moment. Polarity of Bonds is based on the electronegativity between the bonded atoms. If the electronegativity difference is Between 0 and 0.4, the bond is nonpolar covalent. Between 0.5 and 1.8, the bond is polar covalent. Greater than 1.8, the bond is ionic, and the electrons are considered transferred.  Nonpolar Covalent Bonds A nonpolar covalent bond occurs between nonmetals. It is an equal or almost equal sharing of electrons by the two bonding atoms. has a very small electronegativity difference between atoms. (0-0.4) Examples Electronegativity Atoms Difference Type of Bond N-N 3.0 − 3.0 = 0.0 Nonpolar covalent Cl-Br 3.0 − 2.8 = 0.2 Nonpolar covalent H-C 2.5 − 2.1 = 0.4 Nonpolar covalent  Polar Covalent Bonds A polar covalent bond occurs between nonmetal atoms. It is an unequal sharing of electrons. has a moderate electronegativity difference.(0.5-1.8) Examples Electronegativity Atoms Difference Type of Bond O-Cl 3.5 − 3.0 = 0.5 Polar covalent Cl-C 3.0 − 2.5 = 0.5 Polar covalent O-S 3.5 − 2.5 = 1.0 Polar covalent dipole moment (μ) μ = size of the charge × the distance between the charges A dipole moment is reported in a unit called a debye (D) The direction of dipole is represented by ▪ Symmetrical molecules, therefore, have no dipole moment. net net net net μ=0 μ=0 Classification of carbon atoms Classification of hydrogen atoms Hydrogen atoms are also classified in this manner. Primary hydrogens (1o) are attached to carbons bonded to one other C atom Secondary hydrogens (2o) are attached to carbons bonded to two other C’s Tertiary hydrogens (3o) are attached to carbons bonded to three other C’s  sp3 sp2 sp % of S 25% 33% 50% Bond length Longest (1.34 A) Shortest (1.54A) (1.2 A) Bond strength Weakest Strongest C-H electro Lowest Highest negativity C-H acidity Lowest Highest Example Ethane Ethylene Acetylene  Structural Factors Influencing Acidity There are many factors that have effect on the acidity of a proton, one important factor is; The electronegativity of the atom from which the proton is lost.  Factor 1: Electronegativity of A in (H–A) ❖ The acidity of H–A increases as the electronegativity of A (atom connected to the H) increases going from left to the right in the periodic table:  Factor 2: Inductive Effects and acidity Nearby electronegative atoms have effect on the acidity of a proton. As the number of nearby electronegative atoms increases, acidity increases Electronegative atoms pull electron density towards themselves (inductive effect) , increasing the partial positive charge on H Problems Which is the strongest acid?  Factor 3: pKa value As Pka increase, acidity decreases→ pka and acidity are inversely related  Physical properties of organic compounds: Boiling point, melting point and solubility Phenomena explained by van der Waals Forces Increasing molecular weight, so Vander Waals forces increase, and boiling point increase Intermolecular Forces (Non covalent Interaction) T or F: Van der Waals forces can indeed produce temporary dipoles? Phenomena explained by van der Waals Forces 2. Dipole-Dipole forces. 3. Ion-Dipole Forces. 4. Hydrogen Bond Forces Phenomena Explained by hydrogen bond forces: HOW THE STRUCTURE OF A COMPOUND IS REPRESENTED ❖ Lewis Structure: Chemical symbols we have been using, in which the valence electrons are represented as dots or solid lines, are called Lewis structures. ** Lone-pair electrons are umber of nonbonding electrons number of nonbonding electrons Q: Give each atom the appropriate formal charge ❖ CondensedStructures Condensed Structures are like Lewis structures except lone pair of electrons are normally omitted. Structures are often further simplified by omitting some or all covalent bonds 3. Skeletal 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.  Does anyone have any questions? Thank you!