There are five patterns for pushing arrows when drawing resonance structures in Chapter 2.
We were able to draw resonance structures with those five patterns.
There are once again patterns for arrow pushing with ionic mechanisms.
There are only four patterns this time.
The first of these four patterns has already been seen.
One curved arrow is needed to show the attack.
The head and tail of the arrow are placed on opposite sides of the body.
Even though this example uses two curved arrows, there is only one thing happening here: a nucleophile is attacking an electrophile.
We already talked about this pattern in Section 3.8.
At least two curved arrows are required for the transfer steps.
One curved arrow shows the base attacking the proton, and the other shows the acid being converted into its conjugate base.
Make sure you draw both of the curved arrows when drawing a proton transfer step.
The second curved arrow shows the formation of the conjugate base.
There is one more issue to consider before we move on to the next pattern.
We have seen two of the four patterns so far.
In Section 9.4, we will explore this important question more fully.
Good leaving groups are weak bases.
It is an excellent leaving group if iodide is a weak base.
hydroxide is a poor leaving group because it is a strong base.
The leaving group is ejected from the starting alkyl chloride.
It is very common to see the leaving group being ejected during this type of step.
The step is referred to as "loss" of a leaving group.
The leaving group can remain tethered to the starting compound even after it leaves.
The C--O single bond is broken in this example.
The leaving group is made up of alcohol and R is the rest of the structure.
Even though the leaving group remains tethered to the newly formed carbocation, this step would be classified as the loss of a leaving group.
Three of the four patterns have been seen by us.
In this course, we will most likely see one type of rearrangement called a carbocation rearrangement.
There is a change in the location of the electron deficient center.
In the next section of this chapter, we will discuss carbocation rearrangements.
There are only four arrow-pushing patterns for ionic mechanisms.
Each ionic mechanism will have a sequence of arrow-pushing patterns.
There are three steps to this mechanism, in the order in which they are taken.
This mechanism has three steps, in order of priority: 1) protons transfer, 2) loss of a leaving group, and 3) nucleophilic attack.
Both reactions share the same sequence of events.
Two reactions can be seen under a single umbrella.
A proper understanding of reaction mechanisms will unify seemingly different reactions, and you will be able to predict how and when electrons will flow, using the four arrow-pushing patterns, together with a short list of rules and principles.
Two arrow-pushing patterns can be drawn in a single step.
The same time as the loss of a group.
We will look at S 1 and S 2 processes in more detail in Chapter 9.
The arrow-pushing patterns are in ionic mechanisms.
The first step of this process is the removal of a protons from H O+.
The drawing doesn't represent a new step.
resonance does not represent a physical process.
Nothing is happening here.
If you label this as a step of the mechanism, it will be seen as a step of the mechanism.