The chemical reactivity of organic molecules come from their FUNCTIONAL GROUPS

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Regardless of size!

Carbon-hydrogen backbones can stand alone…

…or they can combine with other elements like O,N,S,Cl,Br,F, etc…

… and each combination will have distinct physi-chemical properties.

Solubility (polar? Nonpolar?) Reactivity (pi bonds? Steric

hindrance? Etc..) Stable in acids? Bases? Reactive

with…? Electronegative-electropositive

regions:

Section 3.5-3.9: Organic Reactions

CH21 – 12.10.13 , R.D. Bolinas

Moving onto alkenes and alkynes, and other functional groups, we now have more reactive species. Why?

Four major types of Organic Reactions:

ADDITION REACTIONS: reactants combine without anything leaving to form a product.

ELIMINATION REACTIONS: reactant usually gives off atoms/has leaving groups. The product usually becomes more unsaturated/ forms a double/triple bond.

SUBSTITUTION REACTIONS: reactants exchange groups, like –H and others to give two new products

REARRANGEMENT REACTIONS: one reactant reorganizes its own bonds to form an isomer.

Exercise: IDENTIFY!

catalyst

Exercise: IDENTIFY!

Reaction Mechanisms

Knowing the reaction type is just the beginning.

To really appreciate how we form our products and what we form, we need to study REACTION MECHANISMS

Reaction Mechanisms

“A mechanism describes what takes place at each stage of a chemical transformation—which bonds are broken and in what order, which bonds are formed and in what order, and what the relative rates of the steps are.”

Reaction Mechanisms

Reaction mechanisms entail the movement of electrons

The movement of electrons can be…

Between TWO molecules that collide with each other

In pairs (polar reactions)

WITHIN ONE molecule (internal)

Unpaired/solo (RADICAL reactions)

The two major overarching mechanisms use arrows to show this…

Radical reactions have: initiation, propagation, then termination steps.

Initiation: Chemical bond breaking occurs. This can sometimes be done with RADIATION. The breaking bond makes free radicals.

PROPAGATION: BOTH Chemical bond breaking and forming occurs. When a single radical reacts with a normal compound, one product will still be a free radical.

TERMINATION: TWO free radicals can pair up their unpaired electrons to finally form a stable covalent bond. This ends the reactions.

Polar processes are the more common mechanism

Recall electronegativity and polarity Recall how many functional groups

have atoms that can make them polar

Recall also how opposite charges attract

In polar mechanisms, electrons move from Nucleophile to Electrophile.

Nucleophiles (Nu) – “Nucleus-loving” attracted to positive charges because it is

RICH IN ELECTRONS/ negative

Electrophiles (E) – “Electron-loving” attracted to negative charges because it is

POOR IN ELECTRONS/ positive

Note that neutral compounds can often react either as nucleophiles or as electrophiles, depending on the circumstances. (e.g. H2O)

Exercises: follow the arrow!

TOO LAZY to make this white.

Sample mechanism, and how to analyze and follow it

The mechanism is noted as an ELECTOPHILIC ADDITION

Which is the Nucleophile? The Electrophile?

When we plot ENERGY DIAGRAMS, we can match a mechanism with THERMODYNAMIC INFO.

Terms to remember

Reactants = where we start.Transition states = the in-

betweens usually with bonds halfway broken and half-formed, and are almost impossible to isolate.

Intermediates = another kind of in-between but more of a quick “rest-stop” form we can sometimes isolate and identify. It has its own structure (no “half-bonds”)

Terms to remember

Activation Energy = shown as the height of a hump RELATIVE TO WHERE THE BASE IS (either the products-level or an intermediate-level). This is the energy needed to be overcome for the reaction to move forward.

Terms to remember

Total Energy Change = this is the change in energy level from reactants to products.

A positive one (going net up) means it is ENDOGENIC and absorbs energy, so it is not as favorable.

A negative change (going net down) means the reaction is EXOGENIC and releases energy as the reaction progresses and is more favorable.

Catalysts

LOWER ACTIVATION ENERGY!

DIFFERENT PATHWAY/ MECHANISM

Exercises: Draw the arrows

YOU CAN DO IT! ^____^

OMGWTH?!!?!

The chemical reactivity of organic molecules come from their FUNCTIONAL GROUPS

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