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SC CHEM 333 - Exam 2 Study Guide

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Exam #2 Study Guide Lectures: 8 - 15Lecture 8 (September 17)Constitutional isomer: same molecular formula but different connectivity- Understand what a constitutional isomer is and be able to identify them if given pictures ofmoleculesNaming Alkanes:- Unbranced alkane: # + aneo Example: n-pentane, n-nonane- Branched alkane: Find longest continuous chain and use the root as its nameo Know and be able to recognize and name common substituents:MethylEthylPropylIsopropylIsobutylSec-butylTert-butylo If there are substituents:Name and number each substituentNumber the chain so that the substituent has the lowest number possibleIf there are two or more identical substituents: Number the chain so that the substituent that occurs first gets the lowest numberIf there are two or more different sub-stituents: CHEM 333 1st Edi-tion• List the substituents in alphabetical order. Number the chain so thatthe first substituent encountered gets the lowest number possible.o Remember that di, tri, tetra, etc. are not included in alpabetizingo When there are many substituents, remember to choose the chain that allows it to have the most substituents on itNaming Cycloalkanes:- Cyclo + prefix for number of C + aneo Example: cyclopentane, cyclononane- If there is one substituent, there is no numbero Example: methylcyclopentane- If there is two substituents, list alphabetically- If there is three substituents, list alphabetically and number with the lowest numbers pos-sibleo Example: 2-ethyl-1,4-dimethylcyclohexaneNaming Alkenes/Alkynes:- Be able to name these using similar rules to how to name alkanesClassifying Carbons:- Primary 1°: carbon attached to 1 C- Secondary 2°: carbon attached to 2 C’s- Tertiary 3°: carbon attached to 3 C’s- Quarternary 4°: carbon attached to 4 C’sLecture 9 (September 24) Newman Projections:- Know how to drawo o The “Y” shape denotes front C and substituentso The circle denotes back C with 3 lines off of it for substituentso Dihedral angle: Angle between C-H bond on front C and C-H bond on back Co Understand staggered versus eclipsed positionsEclipsed: conformation where front H eclipses back HStaggered: conformation furthest apart- Know how to draw a relative energy diagram along 360 degree rotations for different New-man Projections. Use knowledge of which conformations are higher in energy over other conformations to fill in the energy diagram that is given.Strains of Conformations:- Know how to identifyo Torsional strain: from eclipsing interactionso Steric strain: when nonbonded atoms separated by four or more bonds are forced closer than atomic radius will allowo Angle strain: bond angle is expanded or compressed from its optimal valueGauche: two substituents (one on front C, one on back C) with a 60 degreeangle. Do not look at hydrogens, only substituents. Gauce interactions are unfavorable/higher energy interactions.Anti: two substituents are 180 degrees apartLecture 10 (September 26)Cyclohexane Conformations:- Know how to draw chair conformation, which has 109.5 degree angle and does not have angle or torsional strain- Understand the difference between axial and equitorial positionso If asked to draw the chair conformation and given a compound drawn with wedges and dashes, if the element is on a wedge, it will always be facing “up.” If the element is on a dash, it will always be facing down. This will help you deter-mine if it is axial or equitorial depending on where you draw it on the chair.- Know other conformations of cyclohexane:o Know the energies of the other conformations and be able to compare them toone another- Know how to draw chair with ring flipo Be able to identify the more stable conformation If there is only one substituent, the conformation with it in the equtiorial position is most stableIf there are two substituents, the conformation with them both in the eq-uitorial position is most stable• If both substituents cannot be in the equitorial position and one is equitorial and one is axial, the one with the larger substituent in the equitorial position is more stable- Know the difference between cis and transo cis: substituents on same side of ringo trans: substituents on opposite side of ring(cis on left, trans on right)Lecture 11 (October 1) Properties of Alkanes:- Not polar - not miscible with water- Good for oxidizing -> burn -> fuel- Number of carbons affects state of alkane:o 1 C to 4 C: gas at room temperature (cooking fuels)o 5 C to 17 C: liquid at room temperature (gas)o 18 C or more: wax at room temperature (candles)- The higher the molecular weight, the higher the boiling pointo Larger molecules = higher boiling point = more surface area, therefore, stronger interaction/more interactiono Small molecules = lower boiling point = less surface area, therefore weaker inter-action/less interactiono Constitutional isomers that are branched have lower boiling point and lower melting point = less surface area = less interactionSynthesis of Alkanes:- Know how to draw these reactionso Double bond or triple bond is taken away and just becomes a single bondStereochemistry: study of molecules as 3D objects- Know how to tell if something is the same compound, constitutional isomer, enantiomer, or diasteromerso Enantiomers: chiral molecules that have nonsuperposable mirror images of each othero Diastereomer: steroisomers whose molecules are not mirror images of each othero- Understand chiralityo Chirality: the handedness of molecules. Look at mirror images of superposable things. If superposable, not chiral. If not superposable, chiral.Something is not chiral (achiral) if there is elements of symmetryLecture 12 (October 3)Assigning Priority Rules:- The higher the atoms number, the higher the priorityo H < C < N < O < S < Cl < Br < I- If there is a tie, go the the next atom. Break the tie at the first point of difference.- If 2 carbons have the same atom of same priority, the one that has more wins.- Double/triple bonds: bonded to equivalent number of “phantom atoms” by single bondsoExamples:(phantom atoms act like atom is bound to it for priority rules)Assigning R or S:- Locate chiral center and assign priorities- Put lowest priority away from you- Find directionality of 3 other groups (clockwise or counterclockwise). Clockwise is R, coun-terclockwise is S.Finding number of stereoisomers:- If there are two or more chircal centers:o n = # of stereogenic centerso # of


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