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C. Chemistry Flashcards

1
Q

How do you calculate formal charges?

A

FC= VE – (b+ lone elctrons)

Where b is number of bonds

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2
Q

Priority groups in descending order:

A
  1. Quaterary ammonium cation suffix: ammonium
  2. Quaternary phosphonium cation suffix: phosphonium
  3. Teriary sulphonium cation suffix : Sulphonium
  4. Carboxcylic acid suffix: -oic acid
  5. Acid anhydride suffix: -oic anhydride
  6. Ester suffix: alkyl -oate
  7. Acyl halides: -oyl halide
  8. Primary amide
  9. Secondary amide
  10. Teriary amide
  11. Nitrile suffix: -nitrile prefix: cyano-
  12. Aldehyde suffix: -al prefix: formyl-
  13. Ketone suffix:-one
  14. primary alcohol
  15. secondary alcohol
  16. tertiary alcohol
  17. primary amine
  18. secondary amine
  19. tertiary amine
  20. Ether
  21. alkene
  22. alkyne
  23. halides Prefix:
    Halo-
  24. nitro
  25. alkanes suffix: -ane prefix: alkyl-
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3
Q

How does sp3 hybridisation work?

A
  1. Promotion of one elctron from s orbital to p orbital
  2. hybridisation-where the orbitals mix to form hybrid orbitals with different energy
  • sp3= s+p+p+p
  • therefore 25% s and 75% p so the hybrid orbitals are closer to the p orbitals as 2s is promoted to a higher energy level
  • so all the p orbitals are used and the s orbital
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4
Q

How doe sp2 hybridisation work?

A
  1. Promotion of one elctron from s orbital to p orbital
  2. hybridisation-where the orbitals mix to form hybrid orbitals with different energy
  • sp2= s+p+p
  • therefore 33% s and 67% p so the hybrid orbitals are closer to the p orbitals as 2s is promoted to a higher energy level
  • so two p orbitals are used and the s orbital this means that there is p orbital which is not used.
  • valence electrons left in the p-orbitals form Pi bonds.

hybridised orbitals form the sigma bonds .

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5
Q

How does sp hybridisation work?

A
  1. Promotion of one elctron from s orbital to p orbital
  2. hybridisation-where the orbitals mix to form hybrid orbitals with different energy
  • sp= s+p
  • therefore 50% s and 50% p so **the hybrid orbitals are inbetween p orbitals and 2s
  • 2s is promoted to a higher energy level**
  • so one p orbital is used and the s orbital this means that there are 2 p orbitals which is not used.
  • valence electrons left in the p-orbitals form Pi bonds.

The hydbrised orbitals form sigma bonds.

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6
Q

How do sigma bonds form?

A

head on overlap of s orbitals or overlap hybrid orbitals

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7
Q

How do Pi bonds form?

A

Side on overlap of p orbitals

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8
Q

How strong is a C=C bond compared to a C-C bond?

A

Less than twice a strong because Pi bonds are weaker than sigma bonds.

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9
Q

What does conjugated mean?

A

Double bonds (or triple) seprated by a single bond or lone pairs adjacent to a double bond, which can be conjugated (delocalsied into a sysem)

NB some lone pairs are in hybridised orbitals so they can’t participate in resonance

it stabilises molecules as they always want a lower energy

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10
Q

What is the relationship between light and conjugated compounds?

A

The longer the conjugated system, the longer the wavelength of light absorbed

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11
Q

How does the colour of the conjugated compound occur?

A

The compound absorbs a certain frequency of visible light and appears as the complementary colour it absorbed.

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12
Q

What are the complementray colour pairings?

A

RED-GREEN
Orange-Blue
Yellow-Purple

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13
Q

What effect does conjugation have on structure?

A

An extended Pi bond is formed and e- are delocalised throughout extended Pi bonds.

Forcing the molecule to be planar

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14
Q

If there are many resonance structures which can be drawn for a compound then it is said to be…

A

highly resonance stabilised

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15
Q

How do you determine if a compound is aromatic?

A

It must:
1. Be cyclic
2. planar
3. COMPLETELY conjugated
4. have (4n+2)Pi electrons

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16
Q

If ANY ONE of the criteria for aromaticity is NOT satisfied then the compound is said to be…

A

Non-aromatic

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17
Q

If the compound satisfies the first 3 criteria for aromaticity but has 4n electrons then the compound is said to be…

A

anti-aromatic (destabilised)

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18
Q

What is the meaning of a conformation?

A

The different spatial arrangement of atoms or molecules that arises by the means of rotation about a c-c single bond.

19
Q

What is a configuration?

A

The relative position of atoms or molecules can only be changed by cleaving and forming new bonds.

20
Q

What is kinetics

A

The study of rates of reactions

21
Q

What is thermodynamics?

A

A description of energy and how it is transferred between all systems

22
Q

How do you measure reaction rates?

A
  • Measuring concs. of products different times
23
Q

what is rate of reaction?

A

the change in conc of a species per unit time OR rate of change in conc of a species

24
Q

Why do reactions get faster with increase in temp

A

greater proportion of molecules have E> or equal to activation energy so more frequent successful collisions

25
Q

what are the 4 laws ofthermodynamics?

A

zeroth-if two bodies, A B, are at thermal equilibrium and two bodies B and C are at thermal eq. then so must A and C
1st- conservation on energy
2nd- entropy
3rd- absolute zero temperature

26
Q

What do ‘heat and work’ refer to in terms of energy?

A

the transfer of energy

27
Q

Define ‘Work’

A
  • the energy transferred from one store to another or the movement of an object caused by a force. =force x distance
28
Q

Define Heat

A

the transfer of energy due a difference in temperature, from hot to cold

29
Q

What is internal energy?

A

The total energy IN a system (regardless of how it got there e.g. work, heat) at a certain moment in time

30
Q

what are the two formulae for change in internal energy and explain the second

this is law 1 of thermo

A

1) delta U= Uf-Ui
2) deltaU=q+w
3)because delta U tells us nothing about how the energy got there in the first place so it may be there due to work/heat DONE on the system

31
Q

When there is no work done (in a closed system with constant volume) what can the formula for internal energy be simplified to?

A

Delta U =q
q=C x deltaT
where C is heat capacity-the amount of heat needed to be absorbed to raise the temp by 1K

32
Q

In a perfect cyclinder piston

W=-opposing force x distance
(pressure=f/A)
so
W=-Patm x A x distance moved (h)
W=-Patm x delta V

A
32
Q

enthalphy, for gases, from first law

since W=-P x del.V
and del.U=q+w

q=del.U-w
q=del.U-(-P x del. V)

therfore q= del.U +Pdel.V
by definition this is enthalpy so
Enthalp change = U +PV

A

this is in a open system and at a constant pressure so energy is transferred as expansion work. Enthalpy = Heat content of an open sysytem

33
Q

What are the Standard conditions for unmixed subs and gases

A
  • 298K, 1atm-subs
  • 273K, 1atm-gases
34
Q

Hess Law

A

The total enthalpy change during a chemical reaction is independent of the intermediate stages and depends only on the nature and state of the reactants and of the products.

35
Q

second law thermo

A

isolated sys=entrpy increases in the course of a spontaneous event

open sys= spontaneous processes include those that increase entropy for universe

36
Q

change in entropy = q/T

where q is the heat energy done to surroundings and T is the temp of surroundings

A

The third law

37
Q

entropy of a perfectly crystalline material is 0 at T=0 K

so no disorder at all and thermal motion

A
38
Q

what is free energy

A

maximum non-expansion work done at constant pressure and temp

g=0 system is at eq

39
Q

gibbs = -RTlnk
where k is eq constant

effect of different reaction conditions e.g. at equilibrium

A
40
Q

Why are antiaromatic compounds less stable than aromatic compounds?

A

they have higher energy

41
Q

What is collision theory?

A

for reactions to happen particles must:
-collide
-collide with sufficient energy ( E>Ea)

42
Q

how do you calculate half life? and life time?

A

T1/2= 0.693/k

where k is the rate constant

lifetime= 1/k

43
Q
A

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