Experiment 1 Pre-Lab Questions

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Songhee Back (1005945694) Experiment 1 Pre-Lab Questions 1. For the series of boron trihalides BX 3 (X = F, Cl, Br, I), rank them in the order you expect for increasing Lewis acidity based solely off arguments of electronegativity. Why do you expect this order? a. BI 3 < BBr 3 < BCl 3 < BF 3 b. According to the arguments of electronegativity, higher electronegativity is associated with a stronger Lewis acid. The more electronegative elements can take up greater number of electrons, increasing the Lewis acidity. Thus, as the electronegativity increases from bottom to top in groups, iodine is the weakest Lewis acid while fluorine is the strongest Lewis acid. 2. Using VSEPR theory, predict the molecular geometries of BX 3 , [BF 4 ] – , [FBX 3 ] – (X = Cl-I), COF 2 and [COF 3 ] – , and suggest the hybridization of each atom within valence bond theory. a. BX 3 i. Molecular Geometry: Trigonal Planar ii. Hybridization of B: sp 2 b. [BF 4 ] – i. Molecular Geometry: Tetrahedral ii. Hybridization of B: sp 3 c. [FBX 3 ] – i. Molecular Geometry: Tetrahedral ii. Hybridization of B: sp 3 d. COF 2 i. Molecular Geometry: Trigonal Planar ii. Hybridization of C: sp 2 e. [COF 3 ] – i. Molecular Geometry: Tetrahedral ii. Hybridization of C: sp 3 3. For the Lewis acid-base adducts, H 3 N---BX 3 , what is the highest symmetry point group possible? What point groups do you expect for the species BX 3 , [BF 4 ] – , [FBX 3 ] – (X = Cl–I), COF 2 and [COF 3 ] – ? a. H 3 N---BX 3 i. C 3v b. BX 3 i. Point Group: D 3h c. [BF 4 ] – i. Point Group: T d d. [FBX 3 ] – i. Point Group: C 3v e. COF 2 i. Point Group: C 2v f. [COF 3 ] – i. Point Group: C 3v

Songhee Back (1005945694) Experiment 1 Pre-Lab Questions 4. Describe in detail one experimental method for measuring relative Lewis acidities. Provide the original literature citation for the method. Hint: there are three different methods available. a. Haartz, J.C., & McDaniel, D.H. (1973). Fluoride ion affinity of some Lewis acids. Journal of the American Chemical Society , 95 (26), 8562-8565. b. Fluoride ion affinity method can be used to measure the relative Lewis acid strength of a chemical compound. In this method, the Lewis acid undergoes a reaction with a fluoride ion, and the energy released is measured. This energy signifies the binding affinity of the Lewis acid against a single base. 5. What are “Frustrated Lewis Pairs” and what are some promising applications? Provide at least one example citing the literature. a. Stephen, D.W. (2015). Frustrated Lewis Pairs. Journal of the American Chemical Society, 137 (32), 10018-10032. b. A Frustrated Lewis Pair is a special type of adduct that is formed from the reaction between a Lewis acid and a Lewis base. In this molecule, the electron pair of the Lewis base is shared, forming a coordinate bond that ultimately lowers the overall energy. According to the 2015 article, the further research in Frustrated Lewis Pairs will lead to a new method for reducing functional groups. Particularly, Stephen highlights the possibility of “metal-free FLP aromatic reductions,” indicating that it will be a new pathway for polycyclic amine natural products.

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