Steps for Drawing Mechanisms - Organic Reactions & Mechanisms (8.4)

Question 1

What is a mechanism?

Answer 1

A reaction mechanism is the step by step sequence

Question 2

What do the arrows mean in mechanisms?

Answer 2

How electrons move to make & break bonds

Question 3

What is the abbreviation for a nucleophile?

Answer 3

Nu

Question 4

What is the abbreviation for an electrophile?

Answer 4

E

Question 5

Give the main features of nucleophiles

Answer 5

• An electron rich substance
• Negatively charged OR lone pair of electrons
• Attracted to an area of low electron density (positive/partially positive charge)

Question 6

Give the main features of electrophiles

Answer 6

• An electron poor substance
• Positively charged
• Empty orbital
• Attracted to an area of high electron density (negative/partially negative charge)

Question 7

What partial charge would areas with more electrons have?

Answer 7

Slightly negative

Question 8

What partial charge would areas with less electrons have?

Answer 8

Slightly positive

Question 9

Organic molecules are usually highly stable when charged. True or false?

Answer 9

True

Question 10

What do curly arrows represent?

Answer 10

They show the movement of electrons - go from an area of negative charge to the area of positive charge

Question 11

Which two atoms can temporarily form extra bonds?

Answer 11

N & O

Question 12

What needs to happen if you make an extra bond to C?

Answer 12

Another bond must break

Question 13

Where should the curly arrow go to when you break a bond?

Answer 13

To break a bond, draw a curly arrow from the bond (where the electrons are) to the more electronegative atom

Question 14

Which type of bond to carbon breaks first?

Answer 14

A double or triple bond

Question 15

If there is no double/triple bond what bond is broken?

Answer 15

The breaking of a bond removes a functional group from the other molecule - this is the leaving group

Question 16

What are the best leaving groups?

Answer 16

• Neutral molecules (e.g H2O)

- Large & electronegative elements (form more stable ions)

Question 17

Put these in order of best to worst leaving groups:
Halogens (top 4 elements)
H2O
-NH2
 -CH3
-C & CH (triple bond)
-H
-OH

Answer 17

(Good leaving groups)
H2O
I-
Br-
(Bad leaving groups)
Cl- 
-H
F-
-CH3
-OH
-C & CH (triple bond)
-NH2

Question 18

List the 7 steps of drawing mechanisms

Answer 18

1. Decide if your reagent is a nucleophile or electrophile
2. Identify areas of partial charge on your substrate that the electrophile may attack
3. Draw a curly arrow between the nucleophile/electrophile and the substrate
4. Consider whether you need to break a bond to make a stable intermediate. Choose the best bond to break & draw a curly arrow
5. Draw the product made by moving these electrons. Account for all of the atoms in the reactants & check the overall charge
6. Decide if your reaction is complete or if you have made an intermediate. Repeat the process again until you have a stable product
7. Draw your product, check your answer

Question 19

If an atom is forced to form fewer bonds than expected, it will usually have…

Answer 19

If an atom is forced to form fewer bonds than expected, it will usually have…
an excess of electrons & be negatively charged

Question 20

If an atom is forced to form too many bonds, it will…

Answer 20

If an atom is forced to form too many bonds, it will…

share its electrons more widely and will be positively charged

Question 21

When a C=C bond breaks, the electrons are…

Answer 21

When a C=C bond breaks, the electrons are…

donated away from the carbon - the carbon has too few electrons & is positive