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CHEM 431 > Lecture 17 (Boron, etc.) > Flashcards

Lecture 17 (Boron, etc.) Flashcards

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1
Q

What does B have a high tendency to form?

A

Cluster bonds (polyhedral cages) in combination with H and, H and C

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2
Q

What kind of reactivity does B have?

A

low reactivity

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3
Q

How B synthesized?

A

reductive methods

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4
Q

What are exo-hydrogen atoms?

A

B-H bond pointing towards the center of the polyhedron

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5
Q

What are endo-hydrogen atoms?

A

Bridging hydrogen atoms

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6
Q

What does n represent in wade-mingos rule?

A

The number of skeletal atoms (vertices) in the cluster

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7
Q

What are closo boranes?

A

boranes with no bridging hydrogen atoms

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8
Q

How many electron pairs in a closo structure?

A

n+1, BnHn^2-, occupy all vertices

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9
Q

How many electron pairs in a nido structure?

A

n+2, BnH(n+4), occupy all but one of the vertices

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10
Q

How many electron pairs in an arachno structure?

A

n+3, BnH(n+6), occupy all but two of the vertices

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11
Q

How many electron pairs in a hypho structure?

A

n+4, BnH(n+8), occupy all but three of the vertices

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12
Q

How do you determine the # of vertices?

A

The number of borons

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13
Q

How do you determine the # of bridging hydrogens?

A

Example. B5H9 reference
vertices= 5
(5BH)= B5H5
H9-H5=4 bridging hydrogens

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14
Q

How do you determine the # of electron pairs?

A

[2(#verticesBH)+1(bridgingH)]/2

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15
Q

What is the name of the deltahedron with 6 vertices?

A

octahedron

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16
Q

What is the name of the deltahedron with 11 vertices?

A

octadecahedron

17
Q

What is the name of the deltahedron with 10 vertices?

A

bicapped square antiprism

18
Q

What happens with higher bonding boranes who are electron deficient?

A

The B in the BH unit is sp hybridized, with two empty p orbitals. On sp hybrid orbital forms the B-H bond, the other is occupied with 2 e- and participates in cluster bonding

19
Q

What is the name of the deltahedron with 12 vertices?

A

icosahedron

20
Q

Boron halides are strong lewis acids. True or false.

A

True

21
Q

What happens to the lewis acid strength of lower group halide elements?

A

The strength increases

BBr3> BCl3> BF3

22
Q

What lowers lewis acidity?

A

Pi characters, and steric replusions

23
Q

What increases lewis acidity?

A

bond strength

24
Q

What is hyperconjugation?

A

the interaction of the electrons in a sigma bond with an adjacent empty (or partially filled) non-bonding p orbital, anti-bonding sigma or pi orbital, or filled pi orbital

CHEM 431 (21 decks)

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