Chemical Reactions Flashcards
Synthesis
A + B -> AB
Decomposition
AB -> A + B
Single replacement
AB + C -> AC + B
Double replacement
AB + CD -> AC + BD
Homolysis
A:B -> A. + B.
Produces radicals
Heterolysis
A:B -> A+ + :B-
Produces ions
What direction do curly arrows represent the movement of electrons?
Site of high electron density to site of low electron density.
sigma- to sigma+
What do full arrows represent?
Movement of a pair of electrons.
What do half arrows represent?
Movement of one electrons.
Where do heterolytic reactions almost always occur at?
Polar covalent bonds
Where do heterolytic reactions almost always occur at?
Polar covalent bonds
What do heterolytic reactions make?
Often assisted by the formation of a new bond to another molecule.
Y + AB -> YA + B
What are the 5 key reaction mechanisms?
- Sn1 Substitution reaction
- Sn2 Substitution reaction
- Addition reactions
- Elimination reactions
- Free radical chain reactions
What is a nucleophilic substitution reaction?
Replacement of one functional group/atom with another negatively charged functional group/atom.
What is a nucleophile?
A chemical species that forms bonds by donating an electron pair.
Draw the mechanism for a nucleophilic reaction
Slide 11 on week 4 of BIOS4006
A = nucleophile
Y = leaving group
What is a Sn1 and Sn2 reaction?
Nucleophilic substitution reaction (double replacement)
What is a Sn1 example reaction?
Reaction between a TERTIARY alkyl halide and NAOH - a 2 step reaction.
What is a Sn2 example reaction?
Reaction between a PRIMARY alkyl halide and NAOH - a 1 step reaction.
What is the difference between Sn1 and Sn2 reactions?
Sn1 = unimolecular
Sn2 = bimolecular
Give an example of a photochemical free radical chain reaction.
Alkyl halide made from a hydrocarbon and halogen gas.
CH4 + Cl2 -> CH3Cl + HCl
Describe the steps for a free radical chain reaction.
Initiation
Propagation
Chain termination
(check slides 23+24)
What is a addition reaction.
2 or more molecules combine to make a larger molecule.
What is an electrophilic addition reaction.
A reaction between an electrophile and nucleophile, adding to double or triple bonds.
What is an electrophile?
An atom/molecule that forms bonds with another atom/molecule by accepting an electron pair.
What is an carbocation?
Ion with a positively charged C atom
What is step A in the first step of electrophilic addition?
+ charge on electrophile is attracted to electron denstiy in double bond.
What is step B in the first step of electrophilic addition?
- As electrophile approaches double bond (of C=C)
- Electrons in A-B bond are repelled towards B
What is step C in the first step of electrophilic addition?
- Double bond breaks, and A binds to C (forming carbocation)
- The two electrons in A-B bond move to B, forming B- ion
What is step A in the second step of electrophilic addition?
B- ion acts as a nucleophile and attacks carbocation.
What is step B in the second step of electrophilic addition?
- The lone pair of electrons on the B- ion are attracted towards the + charged C in carbocation
- Causing B to bond to it
What are the two mechanistic types for elimination reaction?
E1 - 2 step involving an intermediate carbocation
E2 - 1 step
What is hydrolysis?
Involves adding water to one large molecule to break it into multiple smaller molecules.
What is a condensation reaction?
2 or more molecules combine to form a larger molecule, with simultaneous loss of a small molecule (e.g. water).
Term usually reserved for reactions where new C-C bond is formed.
What is esterification?
Process of combining an organic acid with an alcohol to form an ester + water.
acid + alcohol -> ester + water
OIL RIG
Oxidation Is Loss
Reduction Is Gain
What is the oxidation state?
The number of charges an atom would have in a molecle/ion if electrons were transferred completely.
What is the oxidation number of uncombined elements?
0
What is the oxidation number of oxygen (in most compunds)?
-2
Exception: In peroxides it is -1.
What is the oxidation number of hydrogen (in most compounds)?
+1
Exception:
H combined with a metal of lower electronegativity.
What is the oxidation number of halogens?
-1
What is the oxidation number of groups 1,2 and 3?
+1, +2 and +3
What is the oxidation number of carbon?
Vary between +4 to -4.
