Ch 6: Understanding Organic Reactions

Question 1

Substitution reactions involve sigma bonds. One sigma bond breaks and another forms at the ____ carbon atom.

Answer 1

same

Question 2

Elimination is a reaction in which elements of the starting material are “lost” and a __ ____ is formed.

Answer 2

pi bond

Question 3

Addition is a reaction in which elements are added to a starting material. A pi bond is ______ and _ sigma bonds are formed.

Answer 3

broken
2

Question 4

A one-step reaction is called a _________ reaction. No matter how many bonds are broken or formed, a starting material is converted directly to a product.

Answer 4

concerted reaction

Question 5

A stepwise reaction when a starting material is converted to an unstable intermediate, called a ________ intermediate, which then goes on to form the product.

Answer 5

reactive

Question 6

Breaking a bond by equally dividing the electrons between the two atoms in the bond is called _________ or _________ ________.

This process generates uncharged, reactive intermediates with ________ electrons.

Answer 6

homolysis or homolytic cleavage

unpaired

p. 224

Question 7

Breaking a bond by unequally dividing the electrons between the two atoms in the bond is called __________ or __________ __________.

This process generates _______ intermediates.

Answer 7

heterolysis or heterolytic cleavage.

charged

p. 224

Question 8

Carbocations act as __________ and carbanions act as __________.

Answer 8

electrophiles

nucleophiles

Question 9

Bond formation always releases ______.

Answer 9

energy

Question 10

Bond dissociation energy is also called bond dissociation ________ because it refers to the heat absorbed when bonds are cleaved.

Answer 10

enthalpy

Question 11

Because bond breaking requires energy, bond dissociation energies are always ________ numbers, and homolysis is always ___________.

Answer 11

positive
endothermic

p. 228

Question 12

Bond formation always ________ energy, so this reaction is always ____thermic.

Answer 12

releases

exothermic

Question 13

Bond dissociation energies _______ down a column of the periodic table as the valence electrons used in bonding are further from the nucleus.

Answer 13

decrease

Question 14

How can you calculate the overall ΔH° of a reaction?

Answer 14

ΔH° overall (enthalpy change) = (sum of ΔH° of bonds broken) + ((-) sum of ΔH° of bonds formed)

Question 15

What is the activation energy (E_a)?

Answer 15

The energy difference between the starting materials and the transition state.

6. 7
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