Pre-Lab 5

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Emory University *

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203L

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Chemistry

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Dec 6, 2023

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pdf

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Uploaded by ChiefBravery12348

1. (10 Points) For an atom within a molecule to act as a nucleophile, should it have a significant HOMO or LUMO character centered on that atom? A nucleophile, as the name suggests, should be attracted to a nucleus because it contains an electron pair available for bonding. It thus should have a significant HOMO character, i.e. high HOMO, so the electrons in this HOMO are able to attack other positive centers such as a nucleus. 2. (10 points) Calculate the amount of DMAP and CH 3 I you will need to use in your reaction. Note that the molar amounts are included in the experimental procedure. Calculate the grams of DMAP and volume of CH3I. Note that the lab includes the volume for CH3I, but you need to show the calculations here. m(DMAP) = 122.17g/mol * 1mmol * 1mol/1000mmol = 0.12217g v(CH3I) = 141.94 g/mol * 1mmol * 1mol/1000mmol * 1mL/2.28g = 0.0623mL = 62.3uL 3. (10 points) Use Spartan to calculate the energy and molecular orbitals for DMAP. [note, Spartan has this one pre-calculated] Paste in a copy of the HOMO for DMAP (Make sure you set the orbitals to transparent so the atoms can be seen.) What, if anything, does the HOMO tell you about which nitrogen will act as the nucleophile in this reaction? The HOMO itself does not indicate clearly which nitrogen will act as the nucleophile in this reaction since both nitrogen have similar-sized lobes. The HOMO does not predict electron density and fails to tell where electron clouds are located. However, we may recognize that the two CH3 groups around the nitrogen on the right may cause steric hindrance during the reaction. The aromatic nitrogen may thus be a better nucleophile.

4. (10 points) Use Spartan to calculate the energy and molecular orbitals for DMAP. Paste in a copy of the electrostatic potential map for DMAP (Make sure you set the surface to transparent so the atoms can be seen.) What, if anything, does the electrostatic potential map tell you about which nitrogen will act as the nucleophile in this reaction? The aromatic nitrogen will act as the nucleophile in the reaction because it has more electron density (appearing red on the figure above). On the contrary, the other nitrogen on the right has a lower electron density, meaning that it’s a relatively bad nucleophile. Since during the reaction, the lone pairs on nitrogen will attack the electrophile in CH3I, the nitrogen with higher electron density will do the job better. The electrostatic potential can indicate the better nucleophile because it shows the electron clouds clearly. 5. (10 points) Based on what you have learned about NMR, predict what will be the difference in the spectra of the two possible products of this reaction. In other words, based on the 1H NMR, how will you tell if the reaction has followed Path A or Path B? Your answer should discuss number of signals and integration. The number of signals and integration will be different for the two possible products. Based on the following analysis, if the resulting NMR has 4 signals with integration ratio 6:3:2:2, the product is likely to be the second one in the figure. If the resulting NMR has 3 signals with integrations ratio 9:2:2, the product is likely to be the first one in the figure.

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