8.4 Arrow-Pushing Patterns for Ionic Mechanisms

8.4 Arrow-Pushing Patterns for Ionic Mechanisms

  • 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.
    • There are only two steps in this mechanism.
    • The first step was a protons transfer.
    • Water is a base in the final step.