Opposites Attract Relationship within Chemistry: Curved Arrows, Electrophiles, and

Nucleophiles Define the following terms:

Reaction Mechanism:

Nucleophiles :

Electrophiles:

Curved Arrows:

Brosted Lowry Base:

Brosted Lowry Acid:

Carbocation:

Answers:

Reaction Mechanism: a step by step account of all the electrons and bond changes in a chemical reaction.

Nucleophile: a species that shares a pair of electrons with another atom to form a new covalent bond; Lewis base

Electrophile: A species that gains a pair of electrons from another atom to form a new covalent bond; a lewis acid

Curved Arrows: indicate flow of electrons

Brosted Base: Proton acceptor (i.e HO- aka: hydroxide ion)

Brosted acid: Proton donor (i.e H2SO4)

Carbocation: structure with positive formal charge on carbon due to open octet.

Basic Concepts:

Mechanisms: In Chemistry, one of the most important topics is mechanisms. Mechanisms are when two compounds react with each other to form new and different products. Within Mechanisms, the movement of electrons is shown which is quite important since every reaction involves the flow of electron density (electrons are needed to break or form new bonds). To map out the flow of electrons curved arrows are used.

Curved Arrows: These curved arrows indicate how the reaction took place by representing the flow of an electron pair.

Remember that even though these arrows look a lot like the arrows used in resonance, they are not the same!!!

In resonance, the resonance structures do not exist because they are continuously altering from one to another.

In mechanisms, however, the curved arrows actually show the movement of electrons. Each arrow has a tail and a head. The tail is the location of the electrons and the head is where they are going. In other words, it shows the electrons coming from the electron rich area to the electron poor area.

1. Lone pair bond The tail of the arrow shows that the electrons are coming from the oxygen atom and are going to form a bond with the carbon atom, as shown by the head of the arrow.

• Also take note of the changes in formal charge on the oxygen and carbon atom

Electron Source: where electrons are coming from

Electron Destination: where electrons are being moved

TAIL

HEAD

3 possible ways electrons can move: 1. Lone pair bond 2. Bond lone pair 3. Bond bond

wher

*Could be seen as this where the purple dotted line shows the bond that is about to form*

2. Bond Lone Pair

The tail of the arrow is on the bond and the head of the arrow is pointing towards the bromine atom. This indicates that the bond is breaking and those electrons from the bond are going solely towards the bromine atom. This causes the carbon atom to loses one electron, making its formal charge +1 and the bromine atom has gained one electron, making it -1.

3. Bond bond In this process there are usually two arrows which show the flow of electrons. First the blue arrow shows the electrons from the pi bond forming a bond with the hydrogen atom. Then since the hydrogen atom cannot have two bonds, the green arrow shows the electrons going from the bond between hydrogen and chlorine solely to the chlorine atom.

Called A bromide atom (-ide shows (-) charge)

Carbon with positive charge = Carbocation

There can also be mechanisms that have two of the above steps:

Practice Problems In each of the following molecules, classify the arrows shown as one of the three types described above. (bondbond OR bondlone pair OR lone pair bond)

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1.

NEVER show the arrows going in opposite directions because this indicates that the electrons are flowing in opposite directions at the same time.

4.

Answers:

4.

Nucleophilic vs. Electrophilic Many reactions are activated by attraction between opposite charges (Electrostatic). Electrostatics which has to do with this attraction can be described by talking about nucleophiles and electrophiles or in other words something that is electron rich interacting with something that is electron deficient.

Nucleophilic: literally translated as “Nucleus loving”, a species donates its

electrons to electrophiles and forms a covalent bond. It has electron density that is available to share, which is usually in the form of a pi bond or lone pairs or wants to share because of formal charge.

• Electron rich • On the Blunt end of arrow • Lewis base: electron pair donator

o Stronger base=stronger nucleophile • Will usually have pi bonds or lone pairs so that it can form a bond with

electrophiles

Electrophiles: literally translates to “electron loving”, is a species gains electrons from nucleophiles to form a covalent bond. It is electron deficient and wants to gain electrons.

Further details:

• Electron poor which is usually shown by: + charge, open octet • On the pointy side of arrow • Lewis acids: electron pair acceptors

o Bronstead acid is also an acceptor

Practice Problems: Part 1: Classify each compound as Nucleophile or Electrophile.

3.

Part 2: Determine which Compound is the Nucleophile and which is the Electrophile.

1....

4....

2....

5.

4. 3.

1.

2.

Part 3: Complete the Mechanisms by drawing in the appropriate arrows.

Answers:

Part 1: 1.Nucleophile 2.Nucleophile 3.Electrophile 4.Nucleophile 5. Electrophile

Part 2: 1.

3.

Part 3:

2.

4.

Hope this helped!! Good Luck studying!

Works Cited Klein, David R. Organic Chemistry as a Second Language. Danvers: John Wiley, 2004.

Print. Hardinger, Steven. Chemistry 14C Lecture Supplement. 9th ed. Plymouth: Hayden-McNeil,

2011. Print Hardinger, Steven. Chemistry 14C Thinkbook. 6th ed. Plymouth: Hayden-McNeil, 2008.

Print. Google images for many images included in the tutorial