CHEM 2261- Chapter 10 (exam 3) Test
Questions All Answered Correct 2025-
2026 Updated.
what does calculating degree of unsaturation (or unsaturated index) from a molecular formula
determine? - Answer the number of pi bonds and rings in a molecule
what is the unsaturated index formula? - Answer 2C + 2 - H - X + N / 2
what is the IUPAC nomenclature of alkenes and cycloalkenes? - Answer - use longest carbon
chain name (containing the double bond) for the parent name followed by "ene"
- number the longest carbon chain so that the alkene has the lowest number possible (unless
there is a higher priority functional group such as an alcohol which gets lowest number priority).
- indicate the position of the double bon by giving the lowest number of the alkene carbons
- all substituents are alphabetized and follow numbering set by the alkene.
- In a ring, the double bond must be between C's 1 and 2 (unless higher priority functional
group which gets lower number)
- if two or more double bonds present, use Greek prefixes to specify the number (two DB=
diene; three= triene)
can you rotate around the pi bond of an alkene? - Answer - this restricted rotation (also seen
in disubstituted cyclic alkanes) gives rise to cis/trans isomerism (geometric isomers)
what is cis? - Answer Z; Latin for same
what is trans? - Answer E; Latin for opposite
how do you do E/Z nomenclature of alkenes (and cycloalkenes)? - Answer - Cis and Trans
designations are unambiguous and are only for disubstituted alkenes
- in order to name tri- and tetra- substituted alkenes, you must use E and Z designations
- (these can also be used for disubstituted alkenes and rings)
- the priority rules are the same as R,S designations using C-I-P priorities
what is Z? - Answer higher priority groups on the same side of C=C or ring
what is E? - Answer higher priority groups on opposite side of C=C or ring
, what are C-I-P priorities? - Answer highest atomic number gives highest priority.
what are additions of hydrogen halides? - Answer - HCl, HBr, HI
- this reaction takes place in two steps and involves an intermediate carbocation. If it is
symmetrical alkene, only one product is formed
what is the Markovnikov's rule? - Answer the electrophile (H) adds to the sp2 carbon that is
bonded to the greatest number of H atoms
what happens in the addition of HX to an asymmetrical alkene? - Answer - the H
preferentially attaches to the carbon with the greater number of H atoms, and the X (halogen)
preferentially attaches to the carbon with the least number of H atoms (the more stable C+)
what is regioselective? - Answer - the addition reaction
- only one ( or predominantly one) of two possible products is formed if on an achiral carbon.
- the halogen ends up on the more substituted carbon of the double bond as it forms the more
stable C+
- if a chiral carbon forms from the more substituted carbon of the double bond, then a racemic
mixture forms (50% R + 50% S)
what is the addition of water and alcohols? - Answer - water (H2O/ H+)
- alcohols (ROH/H+)
- this hydration reaction has a similar mechanism to that of HX addition (through a carbocation
intermediate) and it is an acid- catalyzed reaction
what is H2O addition to alkenes? - Answer - also regioselective
- follows the Markovnikov's rule
- the more highly substituted alcohol is produced
what is ROH addition to alkenes? - Answer - reacted with alkenes the same way H2O does
- the product is an ether
what happens when certain electrophilic additions do not give the expected major products? -
Answer rearrangement of carbocations
what are the two cases of rearrangement of carbocations? - Answer - apparent addition at a
non-sp2 carbon (1,2-hydride shift)
- change in carbon back bone (1,2-methyl shift)
Questions All Answered Correct 2025-
2026 Updated.
what does calculating degree of unsaturation (or unsaturated index) from a molecular formula
determine? - Answer the number of pi bonds and rings in a molecule
what is the unsaturated index formula? - Answer 2C + 2 - H - X + N / 2
what is the IUPAC nomenclature of alkenes and cycloalkenes? - Answer - use longest carbon
chain name (containing the double bond) for the parent name followed by "ene"
- number the longest carbon chain so that the alkene has the lowest number possible (unless
there is a higher priority functional group such as an alcohol which gets lowest number priority).
- indicate the position of the double bon by giving the lowest number of the alkene carbons
- all substituents are alphabetized and follow numbering set by the alkene.
- In a ring, the double bond must be between C's 1 and 2 (unless higher priority functional
group which gets lower number)
- if two or more double bonds present, use Greek prefixes to specify the number (two DB=
diene; three= triene)
can you rotate around the pi bond of an alkene? - Answer - this restricted rotation (also seen
in disubstituted cyclic alkanes) gives rise to cis/trans isomerism (geometric isomers)
what is cis? - Answer Z; Latin for same
what is trans? - Answer E; Latin for opposite
how do you do E/Z nomenclature of alkenes (and cycloalkenes)? - Answer - Cis and Trans
designations are unambiguous and are only for disubstituted alkenes
- in order to name tri- and tetra- substituted alkenes, you must use E and Z designations
- (these can also be used for disubstituted alkenes and rings)
- the priority rules are the same as R,S designations using C-I-P priorities
what is Z? - Answer higher priority groups on the same side of C=C or ring
what is E? - Answer higher priority groups on opposite side of C=C or ring
, what are C-I-P priorities? - Answer highest atomic number gives highest priority.
what are additions of hydrogen halides? - Answer - HCl, HBr, HI
- this reaction takes place in two steps and involves an intermediate carbocation. If it is
symmetrical alkene, only one product is formed
what is the Markovnikov's rule? - Answer the electrophile (H) adds to the sp2 carbon that is
bonded to the greatest number of H atoms
what happens in the addition of HX to an asymmetrical alkene? - Answer - the H
preferentially attaches to the carbon with the greater number of H atoms, and the X (halogen)
preferentially attaches to the carbon with the least number of H atoms (the more stable C+)
what is regioselective? - Answer - the addition reaction
- only one ( or predominantly one) of two possible products is formed if on an achiral carbon.
- the halogen ends up on the more substituted carbon of the double bond as it forms the more
stable C+
- if a chiral carbon forms from the more substituted carbon of the double bond, then a racemic
mixture forms (50% R + 50% S)
what is the addition of water and alcohols? - Answer - water (H2O/ H+)
- alcohols (ROH/H+)
- this hydration reaction has a similar mechanism to that of HX addition (through a carbocation
intermediate) and it is an acid- catalyzed reaction
what is H2O addition to alkenes? - Answer - also regioselective
- follows the Markovnikov's rule
- the more highly substituted alcohol is produced
what is ROH addition to alkenes? - Answer - reacted with alkenes the same way H2O does
- the product is an ether
what happens when certain electrophilic additions do not give the expected major products? -
Answer rearrangement of carbocations
what are the two cases of rearrangement of carbocations? - Answer - apparent addition at a
non-sp2 carbon (1,2-hydride shift)
- change in carbon back bone (1,2-methyl shift)
