C. Chemistry Flashcards
How do you calculate formal charges?
FC= VE – (b+ lone elctrons)
Where b is number of bonds
Priority groups in descending order:
- Quaterary ammonium cation suffix: ammonium
- Quaternary phosphonium cation suffix: phosphonium
- Teriary sulphonium cation suffix : Sulphonium
- Carboxcylic acid suffix: -oic acid
- Acid anhydride suffix: -oic anhydride
- Ester suffix: alkyl -oate
- Acyl halides: -oyl halide
- Primary amide
- Secondary amide
- Teriary amide
- Nitrile suffix: -nitrile prefix: cyano-
- Aldehyde suffix: -al prefix: formyl-
- Ketone suffix:-one
- primary alcohol
- secondary alcohol
- tertiary alcohol
- primary amine
- secondary amine
- tertiary amine
- Ether
- alkene
- alkyne
- halides Prefix:
Halo- - nitro
- alkanes suffix: -ane prefix: alkyl-
How does sp3 hybridisation work?
- Promotion of one elctron from s orbital to p orbital
- 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
How doe sp2 hybridisation work?
- Promotion of one elctron from s orbital to p orbital
- 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 .
How does sp hybridisation work?
- Promotion of one elctron from s orbital to p orbital
- 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.
How do sigma bonds form?
head on overlap of s orbitals or overlap hybrid orbitals
How do Pi bonds form?
Side on overlap of p orbitals
How strong is a C=C bond compared to a C-C bond?
Less than twice a strong because Pi bonds are weaker than sigma bonds.
What does conjugated mean?
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
What is the relationship between light and conjugated compounds?
The longer the conjugated system, the longer the wavelength of light absorbed
How does the colour of the conjugated compound occur?
The compound absorbs a certain frequency of visible light and appears as the complementary colour it absorbed.
What are the complementray colour pairings?
RED-GREEN
Orange-Blue
Yellow-Purple
What effect does conjugation have on structure?
An extended Pi bond is formed and e- are delocalised throughout extended Pi bonds.
Forcing the molecule to be planar
If there are many resonance structures which can be drawn for a compound then it is said to be…
highly resonance stabilised
How do you determine if a compound is aromatic?
It must:
1. Be cyclic
2. planar
3. COMPLETELY conjugated
4. have (4n+2)Pi electrons
If ANY ONE of the criteria for aromaticity is NOT satisfied then the compound is said to be…
Non-aromatic
If the compound satisfies the first 3 criteria for aromaticity but has 4n electrons then the compound is said to be…
anti-aromatic (destabilised)
What is the meaning of a conformation?
The different spatial arrangement of atoms or molecules that arises by the means of rotation about a c-c single bond.
What is a configuration?
The relative position of atoms or molecules can only be changed by cleaving and forming new bonds.
What is kinetics
The study of rates of reactions
What is thermodynamics?
A description of energy and how it is transferred between all systems
How do you measure reaction rates?
- Measuring concs. of products different times
what is rate of reaction?
the change in conc of a species per unit time OR rate of change in conc of a species
Why do reactions get faster with increase in temp
greater proportion of molecules have E> or equal to activation energy so more frequent successful collisions
what are the 4 laws ofthermodynamics?
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
What do ‘heat and work’ refer to in terms of energy?
the transfer of energy
Define ‘Work’
- the energy transferred from one store to another or the movement of an object caused by a force. =force x distance
Define Heat
the transfer of energy due a difference in temperature, from hot to cold
What is internal energy?
The total energy IN a system (regardless of how it got there e.g. work, heat) at a certain moment in time
what are the two formulae for change in internal energy and explain the second
this is law 1 of thermo
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
When there is no work done (in a closed system with constant volume) what can the formula for internal energy be simplified to?
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
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
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
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
What are the Standard conditions for unmixed subs and gases
- 298K, 1atm-subs
- 273K, 1atm-gases
Hess Law
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.
second law thermo
isolated sys=entrpy increases in the course of a spontaneous event
open sys= spontaneous processes include those that increase entropy for universe
change in entropy = q/T
where q is the heat energy done to surroundings and T is the temp of surroundings
The third law
entropy of a perfectly crystalline material is 0 at T=0 K
so no disorder at all and thermal motion
what is free energy
maximum non-expansion work done at constant pressure and temp
g=0 system is at eq
gibbs = -RTlnk
where k is eq constant
effect of different reaction conditions e.g. at equilibrium
Why are antiaromatic compounds less stable than aromatic compounds?
they have higher energy
What is collision theory?
for reactions to happen particles must:
-collide
-collide with sufficient energy ( E>Ea)
how do you calculate half life? and life time?
T1/2= 0.693/k
where k is the rate constant
lifetime= 1/k
