Chem 331 Orgo 1 Exam 1 Study Guide
Chem 331 Orgo 1 Exam 1 Study Guide CHEM 331
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This 5 page Study Guide was uploaded by Amanda Tobias on Saturday February 6, 2016. The Study Guide belongs to CHEM 331 at Towson University taught by Katherine Bowdy in Winter 2016. Since its upload, it has received 59 views. For similar materials see Organic Chemistry 1 in Chemistry at Towson University.
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Date Created: 02/06/16
[Chem 331] [Dr. Bowdy] [Exam 1 Study Guide] [Chapters # 1 and 2] [Basics] What is Organic Chemistry The Chemistry of Compounds that consist primarily of carbon and hydrogen Not usually natural materials Processed foods, dyes, and medicines are organic compounds Bonding The joining of two atoms in a stable arrangement Bonding leads to lowered energy Bonding leads to increased stability When atoms bond, they are filling their octet which makes them more stable Ionic vs. Covalent Bonds Ionic bonds involve the transfer of electrons from one element to another and are between a metal and a nonmetal Covalent bonds involve the sharing of electrons between two nuclei and are between two nonmetals [Line Bond Structures] All atoms, bond lines, and lone pairs are drawn Memorize bonds and lone pairs of frequently used atoms when neutral Hydrogen has one bond and no lone pairs Carbon has 4 bonds and no lone pairs Nitrogen has 3 bonds and 1 lone pair Oxygen has 2 bonds and 2 lone pairs Fluorine, Chlorine, Bromine, and Iodine have 1 bond and 3 lone pairs Formal Charge Formal charge = # valence electrons all unshared electrons ½ shared electrons If an atom does not have the correct number of bonds and lone pairs that make it neutral, it has a formal charge More electronegative atoms (O, N, F) are more comfortable having a formal charge than less electronegative atoms are (H, C) Exceptions to the octet To break the octet, the atom has to be at least in the third row (S, P, Al) Some small elements may have less than the octet (Group 13) Rules to Line Bond Structures Must contain correct number of electrons Must follow octet rule as appropriate Must contain appropriate formal charges Constitutional isomers Same molecular formula but the connectivity of their atoms is different Resonance structures 2 Lewis structures having the same placement of atoms but a different arrangement of electrons They are not real! An individual resonance structure does not accurately represent the structure of a molecule or ion. Only the hybrid does When drawing the line bond structure, you must draw all resonance structures and the hybrid when asked for all structures When are there resonance structures? When there is a lone pair next to a pi bond When there is a lone pair next to a positive charge When there is a pi bond between two atoms, where one of those atoms is electronegative When there are pi bonds going all the way around a ring [Shorthand Notations] Condensed Structures Not useful for rings Bond lines and lone pairs are not drawn The connectivity is clearly indicated Example: CH3COCH2CH3 Skeletal Structures Carbons and Hydrogens bonded to Carbons are not drawn All heteroatoms (not carbons) and Hydrogens bonded to them are drawn Lone pairs are not generally drawn [Hybridization] What is it? Covalent bonding that forms molecular orbitals from atomic orbitals sp3 hybridization 4 sp3 hybrid orbitals that make sigma bonds Atoms surrounded by 4 groups Groups are atoms and lone pairs If there are 4 atoms surrounding the central atom, its geometry is tetrahedral (109.5 bond angles) If there are 3 atoms and 1 lone pair surrounding the central atom, the geometry is trigonal pyramidal (107 bond angles) If there are 2 atoms and 2 lone pairs surrounding the central atom, the geometry is bent (105 bond angles) sp2 hybridization 3 sp2 hybrid orbitals that form sigma bonds 1 p orbital that forms a pi bond Atoms are surrounded by 3 groups Trigonal planar geometry (120 bond angles) Sometimes the p orbital is empty sp hybridization 2 sp hybrid orbitals that form sigma bonds 2 p orbitals that form pi bonds Atoms surrounded by 2 groups Linear geometry (180 bond angles) Main Point [Bond length, strength, and polarity] Bond length and strength As bond length decreases, bond strength increases Triple bonds are the strongest and the shortest Single bonds are the longest and the weakest Larger atoms have longer bonds, and therefore weaker bonds Sp3 hybridization has the longest and weakest bond sp hybridization has the shortest and strongest bond Polarity When differences in electronegativity result in unequal sharing of electrons, the bond is polar and is said to have a separation of charge or a dipole A dipole is just another word for a polar bond A polar molecule either has one polar bond or two or more dipoles that reinforce each other (water) A nonpolar molecule has either no polar bonds, or two or more bond dipoles that cancel Dipoles cancel if they are of equal strength in opposite directions (CO2) [Acid Base Chemistry] BronstedLowry acids and bases Involves a proton transfer Acids are proton donors Bases are proton acceptors Lewis acids and bases Involves electron transfer Protons are electron acceptors Bases are electron donors Electron rich species react with electron poor species Electronegativity and the polarity of molecules allow us to make predictions about their acid base properties All Bronsted bases are also lewis bases, and all bronsted acids are also lewis acids, but not all lewis acids are bronsted acids pKa The strength of an acid describes its tendency to donate a proton Strong acids ionize completely in water Most acids are weak acids where water is essentially constant so Ka is used The larger the Ka, the stronger the acid pKa = log Ka Most organic compounds have a pKa between 5 and 50 The stronger the pKa, the stronger the Memorize pKa chart! you have to know the order but not the exact pKa Acid Approximate pK a H2SO 4 -9 HCl -7 + H 3 -2 CH 3O H2 5 H2O 16 CH COCH 20 3 3 HC≡CH 25 H2 35 NH 3 40 CH 3H 3 50 Predicting the outcome of Acid Base reactions Equilibrium always favors the formation of the weaker acid and base Identify the acid and base, draw products, and compare the strengths of the acid and conjugate acid. The reaction proceeds towards the weaker one Determining Relative Acid and base strength Factors that increase the stability of the conjugate base increase the acidity of an acid Those factors include: charge, element effects, inductive effects, resonance effects, and hybridization effects The more electronegative the atom, the greater the inductive effect Inductive effects decrease with distance In resonance effects, the acidity of an acid increases when its conjugate base is resonance stabilized: resonance allows delocalization of the negative charge
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