| { |
| "problem_id": "Exam-02-T1", |
| "header": "Problem 1: Carbon Coordination! Since Frankland reported Et_2Zn in 1849, molecules containing carbon-metal bonds have been known and have continually attracted intensive study. Carbon atoms have been found to exhibit a wide variety of electron-donation numbers and coordination numbers when coordinated to metals.", |
| "header_images": [], |
| "subquestions": [ |
| { |
| "sub_id": "Exam-02-T1-1", |
| "tags": [ |
| "1.4", |
| "1.6" |
| ], |
| "text_open": "1-1 For the ligands Ph_3PCPPh_3 (denoted L) and RCR (where R is an alkyl group), state the coordination mode by which each preferentially coordinates to a transition-metal atom.", |
| "text_images": [], |
| "full_mark": 2, |
| "rubric": [ |
| "L preferentially coordinates to a π acceptor, whereas the carbene preferentially coordinates to a π donor. (2 points)" |
| ], |
| "rubric_images": [] |
| }, |
| { |
| "sub_id": "Exam-02-T1-2", |
| "tags": [ |
| "1.1", |
| "1.4" |
| ], |
| "text_open": "1-2 L reacts with ZnI_2 or CdI_2 in a 1:1 ratio, but the products have different structures. The ZnI_2 complex has 2 mutually perpendicular mirror planes and 1 twofold rotation axis but no inversion center. The CdI_2 complex has only 1 mirror plane and 1 twofold rotation axis but does possess an inversion center. Draw both structures.", |
| "text_images": [], |
| "full_mark": 4, |
| "rubric": [ |
| "Structure of the ZnI_2 complex: 'I[Zn]([L])I' (2 points).", |
| "Structure of the CdI_2 complex: '[L][Cd]1(I)I[Cd](I)([L])I1' (2 points)." |
| ], |
| "rubric_images": [ |
| { |
| "file": "Exam-02-T1-2-1-rubric.png", |
| "description": "Schematic structure of the ZnI_2 complex: 'I[Zn]([L])I'" |
| }, |
| { |
| "file": "Exam-02-T1-2-2-rubric.png", |
| "description": "Schematic structure of the CdI_2 complex: '[L][Cd]1(I)I[Cd](I)([L])I1'" |
| } |
| ] |
| }, |
| { |
| "sub_id": "Exam-02-T1-3", |
| "tags": [ |
| "2.1", |
| "2.4", |
| "1.4" |
| ], |
| "text_open": "1-5 As stated in the introduction, carbon atoms can donate different numbers of electrons in complexes. Reaction of WCl_6 with (CH_3)_3CCH_2Li and Ph_2PCH_2CH_2PPh_2 gives a mononuclear W complex containing 3 carbon-tungsten bonds whose lengths are all distinctly different. Write the equation for its preparation.", |
| "text_images": [], |
| "full_mark": 3, |
| "rubric": [ |
| "WCl_6 + 6(CH_3)_3CCH_2Li + Ph_2PCH_2CH_2PPh_2 → 3C(CH_3)_4 + 6LiCl + W(Ph_2PCH_2CH_2PPh_2)[(CH_3)_3CCH_2][(CH_3)_3CCH][(CH_3)_3CC] (3 points)." |
| ], |
| "rubric_images": [] |
| } |
| ] |
| } |
|
|
