Electronic Properties Flashcards

1
Q

what is a conjugated double bond

A

single (sigma) and double (pi) bonds alternate which leads to delocalization of electrons

(belong to a region/group of atoms not a single one)

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2
Q

what does the delocalization of electrons lead to

A

increase in stability of compound

  • due to similar bond length between sigma and pi bonds
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3
Q

What does the decrease in symmetry of MO mean?

A

higher energy

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4
Q

What are resonance structures

A

the alternating structures of a compound (that it can exist in)

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5
Q

What are the rules for generating resonance structures

A
  • movement of electron pairs only (between structures)
  • the less charged, the more favourable
  • no similar charges on adjacent atoms
  • negative charges on electronegative atoms favoured
  • delocalization max in planar system possible
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6
Q

can the bonds be different to each other in a carbon ring?

A

(unless there are double bonds) the bonds are all identical in a ring

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7
Q

Draw the resonance structures of benzene

A
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8
Q

What are two allotropes carbon

A

graphite and diamond

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9
Q

Why is the Benzene structure from Hückels proposal so stable?

A

they have overlapping p orbitals. This means that there are dense electron clouds above and below the horizontal axis

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10
Q

Do orbitals alway have to have electrons in them?

A

no. they can be vacant

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11
Q

Where can electrons be found in an orbital?

A

anywhere except in a node. (in p orbital one electron can be on either side but not in the middle

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12
Q

are orbitals interrelated?

A

No. ther are superimposed. 1s orbital is not middle part of 2s for example. (they are separate)

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13
Q

When is a compound considered aromatic?

A

when it follows Hückel rules:

  • # of pi electrons has to be 4N+2 (N=0,1,2,..)
  • molecule is planar
  • conjugated pi system
  • possible charges have tobe delocalized
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14
Q

What is tautomerism?

A

(constitutional isomers)

An reaction that simply. involes the intramolecular transfer of a protein

real fast equilibrium between two isomers

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15
Q

name and draw 3 examples of an aromatic compound

A
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16
Q

give 2 examples of a tautomeric pair

17
Q

what is an inductive effect (I)?

A

polarization of bonds due to different electronegativity (short range effect)

18
Q

When do we haven a +I Effect?

A
  • electron donation
  • increase of electron density
  • stabilization of electron deficient adjacent centres possible
19
Q

What is an -I Effect?

A
  • electron withdrawel
  • decrease of electron density to stabilize electron rich adjacent centres
20
Q

What are examples of electron withdrawing groups (for inductive effect)?

A
  • NO2
  • F
  • COOH
  • Cl
  • Br
  • I
  • OH
21
Q

What are examples of electron donating groups (inductive effect)?

A
  • Me3C
  • Me2CH
  • MeCH2
22
Q

What is a Resonance (mesomeric) Effect?

A

delocalization of lone pairs of pi bonds between resonance structures

only formal migration of lone pairs and bonds helps visualize densities

23
Q

What is a +M Effect?

A

donation of lone pair

  • stabilization of electron deficient center (increase electron density)
24
Q

What is the -M effect?

A

removal of electron pair

  • stabilizing electron rich centers
25
What are examples of electron accepting groups (-M)
* COOH * COOR * CN * CHO
26
What are electron pushing groups (+M)?
* Cl * Br * I * OH * OR
27
what is Hammets reaction constant ρ?
is a measure of reactions's sensitivity to substituent effect
28
what does a positive rho mean?
more electrons in transition state than in starting material (electron withdrawing group aids)
29
What is hyperconjugation?
**stabilization interaction** that results from the interaction of **electrons in filed orbital** (usally in sigma bond) with a**djacent empty** or partially filled **orbital** to give an extended molecular orbital that increases stability of the system
30