DAMIETTA UNIVERSITY EM-103: BASI RGANI EMISTRY LETURES 1-2 Dr Ali El-Agamey ١ LEARNING UTMES LETURES 1-2 Appreciate the importance of organic chemistry. Draw the structures of organic compounds using Lewis, condensed and skeletal structures. Identify various functional groups. Identify the hybridization of various atoms. ٢
Reading Wade LG, rganic hemistry, Prentice all, Upper Saddle River, 2010. J layden et al, rganic hemistry, xford University Press, 2001. Morrison & Boyd, rganic hemistry, Allyn and Bacon, Inc., Boston, 1987. P Sykes, A Guidebook to Mechanism in rganic hemistry, 1991. ٣ Electronic onfigurations of Atoms Valence electrons are electrons on the outermost shell of the atom. hapter 1 ٤
Bonding Patterns N alides (F, l,, Br, I) Valence electrons # Bonds # Lone Pair Electrons 4 4 0 5 3 1 6 2 2 7 1 3 hapter 1 ٥ Drawing molecules (1) Lewis structure: a structural formula that shows all valence electrons, with the bonds symbolized by dashes ( ) or by pairs of dots, and nonbonding electrons symbolized by dots. (2) ondensed structural formulas: (3) Skeletal structure (Line-Angle Formula): (i) Draw chains of atoms as zig-zags (ii) Show functional groups (iii) Miss out and atoms ٦
Lewis Structures arbon: 4 e 4 @1 e ea: 4 e 8 e 4 Nitrogen: 5 e 3 @1 e ea: 3 e 8 e N 3 N 2 l 2 xygen: 6 e 2 @1 e ea: 2 e 8 e 2 l @7 e ea: 14 e l hapter 1 ٧ l Lone Pairs hapter 1 ٨
Double and Triple Bonds hapter 1 ٩ (2) ondensed structural formulas Lewis (Extended) 1 2 ondensed 3 3 1 2 3 4 3 2 2 3 hapter 1 ١٠
(2) ondensed structural formulas Lewis (Extended) ondensed Br 1 2 3 4 Br 3 2 3 1 2 3 4 2 2 3 hapter 1 ١١ ondensed structural formulas hapter 1 ١٢
ondensed structural formulas hapter 1 ١٣ ondensed structural formulas hapter 1 ١٤
(3) Skeletal structure (line-angle formula) 1 2 3 4 1 2 3 4 5 6 1 2 3 4 5 6 hapter 1 ١٥ Skeletal structure (line-angle formula) hapter 1 ١٦
Problem 1-Draw the complete Lewis structures for the following condensed structural formulas. (i) 3 ( 2 ) 3 ( 3 ) 2 (iii) ( 3 2 ) 2 (ii) 3 (iv) ( 3 ) 2 2 l omework: Give Lewis structures corresponding to the following skeletal structures. N (a) (b) (c) (d) (e) ١٧ omework Draw the skeletal structures for the following Lewis structures. (a) N (b) (c) ١٨
Names of normal alkanes omework: Draw the skeletal structures for the following compounds except methane. 4 Methane 3 ( 2 ) 6 3 ctane 3 3 Ethane 3 ( 2 ) 7 3 Nonane 3 2 3 Propane 3 ( 2 ) 8 3 Decane 3 ( 2 ) 2 3 Butane 3 ( 2 ) 9 3 Undecane 3 ( 2 ) 3 3 Pentane 3 ( 2 ) 10 3 Dodecane 3 ( 2 ) 4 3 exane 3 ( 2 ) 11 3 Tridecane 3 ( 2 ) 5 3 eptane 3 ( 2 ) 12 3 Tetradecane ١٩ R = Alkyl; Ar = Aryl. Functional groups Alkanes Alkenes Alkynes R Alcohols Ar Phenols R Ethers R 1 R N 2 R NR 1 R NR 1 R 2 Amines R X Alkyl halide X = F, l, Br, I ٢٠
Functional groups R R R 1 A l d e h y d e s K e t o n e s R 2 a r b o x y l i c a c i d s R N 2 R R NR 1 R NR R 2 R 1 R 2 1 R l R 1 Amides Acyl chlorides Esters Anhydrides arboxylic acid derivatives ٢١ Functional groups R N or R N Nitriles or cyanides N R or R N 2 Nitro compounds Aromatic hydrocarbons contain benzene ring ٢٢
Problem 1-Draw the skeletal structures for the following compounds and name the functional groups.. (i) 3 ( 2 ) 3 ( 3 ) 2 (iii) ( 3 2 ) 2 (ii) 3 (iv) ( 3 ) 2 2 l omework: Identify the functional groups in the following structures. N N (a) (b) (c) ٢٣ Electronic Structure of the Atom An atom has a dense, positively charged nucleus surrounded by a cloud of electrons. The electron density is highest at the nucleus and drops off exponentially with increasing distance from the nucleus in any direction. hapter 1 ٢٤
There are three 2p orbitals, oriented at right angles to each other. Each p orbital consists of two lobes. Each is labeled according to its orientation along the x, y, or z axis. The 2p rbitals hapter 1 ٢٥ Electronic onfigurations Electronic configuration of carbon The aufbau principle states to fill the lowest energy orbitals first. und s rule states that when there are two or more orbitals of the same energy (degenerate), electrons will go into different orbitals rather than pairing up in the same orbital. hapter 1 ٢٦
ybridization Experimental results show that the bond angles of 2 and N 3 are roughly tetrahedral (104 o and 107 o respectively) and 4 is exactly tetrahedral (109.5 o )!!! Problem: rbitals available for bonding are 2s () and 2p (right angles to each other) In order to account for the observed geometry, hybridization was proposed as a convenient model. ybridization of atomic orbitals is a mathematical mixing of two or more different orbitals on a given atom to give the same number of new hybrid atomic orbitals, each of which has some of the character of the original component orbitals. ٢٧ Also, the resulting hybrid orbitals have directional character and when used to bond with atomic orbitals of other atoms, they help to determine the shape of the molecule formed. ybridization involves (i) promotion and (ii) mixing (hybridization), For example; 4 2s 2 2p x1 2p 1 (i) (ii) y 2s 1 2p x1 2p y1 2p 1 z 4sp 3 hybrid atomic orbitals ybridization ٢٨
sp 3 ybrid rbitals There are 4 sp 3 hybrid atomic orbitals. The atoms has tetrahedral electron pair geometry. 109.5 bond angle hapter 2 ٢٩ Bonding in Ethane Ethane is composed of two methyl groups bonded by the overlap of their sp 3 hybrid orbitals. There is free rotation along single bonds. hapter 2 ٣٠
ybridization Ethylene: 2 2 2s 1 2p x1 2p y1 2p z 1 (ii) 3 sp 2 hybrid atomic orbitals and 2p z 1 In ethylene, the whole skeleton is in one plane and the central -bond is above and below the plane. ٣١ sp 2 ybrid rbitals 3 sp 2 hybrid atomic orbitals. Trigonal planar geometry 120 bond angle hapter 2 ٣٢
Bonding in Ethylene Ethylene has three (3) sigma bonds formed by its sp 2 hybrid orbitals in a trigonal planar geometry. The unhybridized p orbital of one carbon is perpendicular to its sp 2 hybrid orbitals and it is parallel to the unhybridized p orbital of the second carbon. verlap of these two p orbitals will produce a pi bond (double bond) which is located above and below the sigma bond. hapter 2 ٣٣ Rotation Around Double Bonds Single bonds can rotate freely. Double bonds cannot rotate. hapter 2 ٣٤
ybridization Acetylene: 2s 1 2p x1 2p y1 2p z 1 2p y1 and 2p z 1 (ii) 2 sp hybrid atomic orbitals plus In acetylene, the whole skeleton is linear. ٣٥ sp ybrid rbitals ave 2 sp hybrid atomic orbitals. Linear electron pair geometry. 180 bond angle. hapter 2 ٣٦
Valence-shell electron-pair repulsion theory (VSEPR) Electron pairs repel each other, and the bonds and lone pairs around a central atom generally are separated by the largest possible angles. An angle of 109.5 o is the largest possible separation for four pairs of electrons; 120 o is the largest separation for three pairs; and 180 o is the largest separation for two pairs. ٣٧ Molecular Shapes As mentioned earlier, bond angles cannot be explained with simple s and p orbitals. Valence-shell electron-pair repulsion theory (VSEPR) is used to explain the molecular shape of molecules. hapter 2 ٣٨
General rules of hybridization and geometry Rule 1: Both sigma bonding electrons and lone pairs can occupy hybrid orbitals. Therefore, The no. of hybrid orbitals on an atom = no. of sigma bonds + no. of lone pairs of electrons The no. of hybrid orbitals on an atom = no. of atoms bonded to the central atom + no. of lone pairs of electrons Rule 2: Use the hybridization and geometry that give the widest possible separation of the calculated number of bonds and lone pairs. ٣٩ General rules of hybridization and geometry Rule 3: If two or three pairs of electrons form a multiple bond between two atoms, the first bond is a sigma bond formed by a hybrid orbital. The second bond is a pi bond, consisting of two lobes above and below the sigma bond, formed by unhybridized p orbitals. The third bond of a triple bond is another pi bond, perpendicular to the first pi bond. ٤٠
Specify the hybridization of each atom in the following compound? 1 2 3 4 5 6 hex-1-en-4-yne 1, 2 are sp 2 ; 3, 6 are sp 3 and 4, 5 are sp More Examples ٤١ What is the hybridization of B 4, 4, N + 4 and + 3? B 4, 4 and N 4+ are sp 3 -hybridized and 3+ is sp 2 - hybridized. B N sp 3 -hybridized sp 2 -hybridized ٤٢
What is the hybridization of N 3, 3, 3 +, and 2? All molecules are sp 3 -hybridized. ٤٣ Energy of various orbitals Electronic configuration of carbon The greater the s character, the lower the energy, the greater stability. Increasing of energy sp sp 2 sp 3 p We need to populate the lowest energy orbital. hapter 1 ٤٤
omework Specify the hybridization of each atom and if the atom has lone pair, specify the type of orbitals which include them? Be 2 B 3 (a) (b) (c) (d) ٤٥ omework Specify the hybridization of each atom and if the atom has lone pair, specify the type of orbitals which include them? N 3 2 2 (a) (b) ٤٦