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"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": []
}
]
}
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