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CHEM 233, Fall 2013 Midterm #1 answer PRINTED FIRST NAME PRINTED LAST NAME Ian R. Gould ASU ID or Posting ID key Person on your LEFT (or Aisle) Person on your RIGHT (or Aisle) BDE 1___________/30 ........ • PRINT YOUR NAME ON EACH PAGE! charges 2___________/18 ........ • READ THE DIRECTIONS CAREFULLY! A.O.s 3__________/22 ........ • USE BLANK PAGES AS SCRATCH PAPER structures 4__________/43 ........ work on blank pages will not be graded... hybrid 5__________/20 ........ •WRITE CLEARLY! dipoles 6__________/20 ........ • MOLECULAR MODELS ARE ALLOWED M.O.s 7__________/22 ........ • DO NOT USE RED INK • DON'T CHEAT, USE COMMON SENSE! Total (incl Extra)________/175+5 Extra Credit_____/5 H He Li Be B N O F Ne Na Mg Al Si P S Cl Ar H/H ~1.0 Me/Me ~0.9 Ga Ge As Se Br Kr H/Me ~1.4 Et/Me ~0.95 In Sn Sb Te I Xe Me/Me ~2.6 i-Pr/Me ~1.1 Tl Pb Bi Po At Rn Me/Et ~2.9 t-Bu/Me ~2.7 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd Cs Ba Lu Hf Ta W small range range of values broad peak Re Os Ir Pt Au Hg O H C N N H C O C Interaction Energies, kcal/mol C H O C H H C N O OR amine R NH2 variable and condition alcohol R OH dependent, ca. 2 - 6 δ 11 220 O 10 200 Aromatic Ar H mainly 8 - 6.5 C CH3 R C OH –H2C NR2 C CH2 9 180 O C 8 160 H O –OCH2– NMR Correlation Charts 7 140 6 120 5 100 R2C Aromatic CR2 C CH 4 80 3 60 2 40 –OCH2– R C N RC H ~15 C C 1500 –H2C X (δ, ppm) ~2 H NR2 1650 2000 H H C 1710 2500 O C H ~8 ~2 C C O 2200 3000 O R C OH H ~10 H 1600 O C O C O H 3500 H C C 1735 CH broad ~3000 (cm-1) ~7 H C 2850–2960 broad ~3300 H 1680 C H broad with spikes ~3300 O H H H C C C 2200 C N O 2720–2820 2 peaks 3000– 3100 N H C 1600–1660 H C 3300 Approximate Coupling Constants, J (Hz), for 1H NMR Spectra Infrared Correlation Chart usually strong C Gauche Eclipsing CR Alkyl 3Y > 2Y > 1Y 1 20 0 0 Alkyl 3Y > 2Y > 1Y C X C NR2 -2- NAME CHEMISTRY 233, Fall 2013, MIDTERM #1 Question 1 (30 pts.) For the C-C bond A, and the C-H bonds B and C indicated by the arrows a) Draw the curved arrow pushing describing homolytic bond cleavage, and draw the products of each homolytic bond cleavage reaction b) Rank the bond dissociation energies for A, B and C and give a brief explanation c) For the C-H bonds B and C ONLY, draw energy versus C-H separation distance diagrams for bond dissociation on the same diagram (use the provided axes), clearly indicate which is which d) Indicate the A magnitudes of the BDEs for B and C on the diagrams H A < smallest BDE H < B largest BDE H H H C H H B H H H C H H C-C bonds are weaker than C-H bonds because they are made by overlap of larger atomic orbitals, which results in poorer overlap, higher energy electrons in the bond, A is the weakest bond the carbon is sp2 hybridized in B compared to sp3 hybridized in C, sp2 hybrid A.O.s are smaller, lower in energy, the electrons in bond B are lower in energy than in C, B is the strongest bond B Energy C BDE (B) BDE (C) rR–H Extra Credit (5 pts.) In the "Organic Chemistry in Real Life" pages, anti-bonding molecular orbitals were described as playing an important role in which of the following color burning hydrocarbons ATP energy conversion -3- CHEMISTRY 233, Fall 2013, MIDTERM #1 NAME Question 2 (18 pts.) Add any missing formal changes to the following structure (all nonbonding electrons are included). H H O N H N N H H O H N H H aqueous solution form of the amino acid arginine Question 3 (22 pts.) Given the following picture of the Ψ for a 3p A.O., give a plot of Ψ versus distance from the nucleus, r (use the provided axes). Indicate the positions of the nodes BOTH on the picture AND on your plot. STATE THE NUMBER OF NODES that the wavefunction for this orbital has (use the nodal theorem). spherical node 2 spherical node 2 r plane node 1 plane node 1 spherical node 2 Ψ 0 r BOTH are equally correct OR r spherical node 2 0 r you did not need to differentiate the spherical and plane nodes, but you did have to know that the total number of nodes was TWO -4- CHEMISTRY 233, Fall 2013, MIDTERM #1 NAME Question 4 (43 pts.) For the molecular formula C4H7N << this was suppsoed to be C3H5N!! a) Give the degrees of unsaturation 2 degrees of unsaturation b) Draw ONE PAIR of stereoisomers that obey the normal rules of valence for each atom. Include all non-bonding electrons. You can draw Lewis structures or line-angle structures (your choice). If you draw line-angle structures, don't forget to include the H atoms that are normally included as part of the functional groups. NH2 NH2 OR and NH2 and NH2 there are many possibilities, too many to list...... c) Draw FIVE ADDITIONAL structural isomers that obey the normal rules of valence for each atom. Include all non-bonding electrons. You can draw Lewis structures or line-angle structures (your choice). If you draw line-angle structures, don't forget to include the H atoms that are normally included as part of the functional groups. DO NOT INCLUDE ANY STRUCTURE YOU INCLUDED AS PART OF YOUR ANSWER TO PART b) OF THIS QUESTION! NH2 NH2 N N N N NH H N N NH N 4-ring structures and 3-ring structures etc. etc. there are many possibilities, way too many to list...... CHEMISTRY 233, Fall 2013, MIDTERM #1 -5- NAME Question 5 (20 pts.) For the oxygen atom in the structure given below, give the hybridization AND make a list of the hybrid atomic orbitals and explain exactly how the oxygen makes use of each one (e.g. it uses X A.O. to make a σ-bond to atom Y, etc.) sp2 H sp2 - makes a σ-bond to hydrogen O sp2 - makes a σ-bond to carbon sp2 - holds the non-bonding pair of electrons p - makes a π-bond to carbon Question 6 (20 pts.) ON TOP OF the structures of acetone and acetonitrile shown below, draw the molecular dipole moments (you should show the direction only, your dipoles do not need to represent their magnitudes). The dipole moment of acetonitrile is LARGER than that for acetone, give a brief explanation for this fact. O + H3C + acetone smaller molecular dipole moment C N acetonitrile LARGER molecular dipole moment π-electrons are more polarizable than σ-electrons, even though N is less electronegative than O, the C-N triple bond has more π-electrons (2 π-bonds compared to 1), and thus the electrons are more polarized, the dipole moment is thus larger Question 7 (22 pts.) For the indicated localized molecular orbitals, draw a picture of the Ψ or Ψ2 as requested, directly ON TOP of the structures. In each case also give the atomic orbitals that are used to "build" the molecular orbitals. All non-bonding electrons are shown. Indicate the positions of any nodes for the Ψ. Indicate where the probability of finding the electrons is zero for the Ψ2. nodes H a) H H C O C - sp3 A.O. O - sp3 A.O. H H Ψ∗ for the C-O bond b) H3C C N zero probability Ψ2 for one of the C-N π M.O.s C - p A.O. N - p A.O.