CHEM 237 1nd EditionMidterm # 1 Study Guide Lectures: 1 - 13This study guide consists of short descriptions of important topics covered in lectures as well as a highlight of what the student should be comfortable with for the test. There are no practice questions in this guide. Please refer to previous lectures, the CHEM 237 webpage, and the textbook for practice questions.Lecture 1 (Sept. 25)You should be able to:- Draw and interpret lewis structures. - Identify how to create a resonance structure and how to draw one.- Identify non-zero charges on atoms and minimize formal charge.Lewis Dot Structures, Resonance, Formal Charge.Lewis dot structures are used to indicate bonding between atoms as well as lone pairs Note thatthis material is review from CHEM 162 and as such will not be focused on in the study guide, butyou should re-familiarize yourself with these terms and concepts if needed.Lecture 2 (Sept. 27)You should be able to:- Draw and interpret bond line drawings and curved arrow notation.- Understand the concepts behind electronegativity.Bond Line Drawing, Curved Arrow NotationBond line drawing is commonly used in organic chemistry in order to simplify the amount of work needed to fully draw an organic molecule. In bond line drawing, carbons are indicated by drawing bent lines, hydrogen atoms are not shown when on carbon, and lone pairs are usually left off. Curved arrows are used to indicate the movement of electrons via the breaking/forming of a bond.Electronegativity, Dipole MomentsElectronegativity indicates the tendency of an atom to attract electrons. Electronegativity increases in atoms as you go up and across the periodic table. The EN difference between atomsin a molecule creates a dipole moment pointing in a certain direction.Lecture 3 (Sept. 30)You should be able to:- Understand and interpret molecular shape based on VSEPR (This should be review from CHEM 162 and will not be focused on in the study guide).- Identify chiral/achiral molecules, chirality centers, and enantiomers.- Calculate optical purity and enantiomeric excess.ChiralityA molecule is chiral if its two mirror image forms are not superimposable on each other. These two forms are known as enantiomers. If the mirror images are superimposable, the molecule is known as achiral. Chirality centers are carbons with four different atoms or groups attached to them. Lines of symmetry can be used to identify achiral molecules, as chiral molecules will not be symmetric about any line.Optical PurityOptical purity refers to amount of enantiomers in a mixture. A 50/50 mix of enantiomers is called a racemic mixture. Optical purity=(rotation of sample)/(rotation of pure sample)*100. Enantiomeric excess = % major enantiomer - % minor enantiomer.Lecture 4 (Oct. 2)You should be able to:- Identify and assign R & S configurations to molecules.- Interpret fischer projections and assign configurations from them.- Interpret how stereochemistry changes based on placement and orientation of substituents.R & S ConfigurationMolecules are assigned an R or S configuration based on the arrangement of atoms or groups around the central atom. This is done by giving substituents priority numbers based on atomic number, and orienting the molecule such that the lowest priority substituent is facing the back of the molecule. The direction that the other molecules are counted in then gives you the R (clockwise) configuration or S (counter-clockwise) configuration.Fischer ProjectionsFischer projections are used to create a 2-D representation of a 3-D molecule. Horizontal lines indicate wedges (bonds facing the viewer) and vertical lines indicate dashes (bonds away from the viewer).Lecture 5 (Oct. 4)You should be able to:- Interpret molecules with more than one chirality center.- Identify diastereomers and mesocompounds.- Understand the different definitions of acids and bases. Memorize the provided list of pKa’s in the chart provided on the webite.Molecules With More than One Chirality CenterMolecules that have more than one chirality center must flip both chirality centers in order to create the proper enantiomer. Flipping only one of the chirality centers creates a diastereomer –a stereoisomer that is not a mirror image and is not superimposable. These types of molecules have 2n configurations, where n is the number of chirality centers in the molecule. Mesocompounds are molecules with more than one chirality center that are achiral. These can usually be identified by looking for lines of symmetry in molecules.Acid-Base ReactionsArrhenius defined acids as H+ and bases as OH-. Bronsted-Lowry defined acids as H+ donors and bases as H+ acceptors. Lewis defined acids as electron pair acceptors and bases as electron pair donors. Keq = [products]/[reactants]. pKa = -log (Ka).Lecture 6 (Oct. 7)You should be able to:- Interpret acid strength based on pKa.- Understand what factors into acidity and how protons are pulled from acids.- Understand and interpret acid-base equilibria.- Approximate Keq from Ka or pKa values.Acid strengthGenerally, a higher pKa indicates a weaker acid. The stronger the acid, the weaker the conjugate base is. The stronger the base, the weaker the conjugate acid is. Acid strength is determined by strength of the H-X bond, bond polarity, and electron delocalization. A stronger bond between an acidic hydrogen atom results in a weaker acid. Molecules that are more polar (have a higher electronegativity difference) are also more polar. Electron delocalization stabilizes molecules, making them weaker bases.Equilibria and Multiple Acidic Hydrogen AtomsEquilibrium tends to favor the weaker acid/base side. When molecules have multiple acidic protons, the proton with the lowest pKa will be pulled off the molecule frist.Lecture 7 (Oct. 9)You should be able to:- Understand how and why hybridization occurs, and how to assign it (this should be review from CHEM 162, and will not be focused on in the study guide).- Identify, name, and draw alkanes as well as recognize constitutional isomers.AlkanesAlkanes are saturated carbons in which there are only single bonds between carbons. They are denoted by the suffix –ane. Prefixes are attached based on the number of carbons in longest chain, and circular chains are denoted with the prefix cyclo-. Constitutional isomers (isomers that have the same molecular formula but different connectivity) exist for chains longer than two carbons. The