Chapter 5.SE, Problem 43AP

Interpretation Introduction

a)

Interpretation:

R and S configuration is to be assigned to the following molecules.

Concept introduction:

Rule 1:

a) Higher atomic number precedes lower.

b) An atom node duplicated closer to the root ranks higher than one duplicated further.

Rule 2: Higher atomic mass number precedes lower.

Rule 3: Z precedes E and this precedes nonstereogenic (nst) double bonds.

Rule 4:

a) Chiral stereogenic units precede pseudoasymmetric stereogenic units and these precede nonstereogenic units (R = S > r = s > nst).

b) When two ligards have different descriptor pairs, the one with the first chosen like descriptor pairs has priority over the one with a corresponding unlike descriptor pairs.

c) r precedes s.

Rule 5: An atom or group with descriptor R has priority over its enantiomorph S.

Answer to Problem 43AP

R configuration

Explanation of Solution

By ranking the substituent in the following examples based on Cahn-Ingold Prelog rules,

R and S configuration can be assigned to the following molecules.

1. Determine the priorities of the four attached groups from highest (1) to lowest (4).

This is the same as in all methods.

2. Draw the steering wheel. Draw a curved arrow around from 1 to 2 to 3 and back to 1 and note which direction this arrow goes, clockwise (cw) or counterclockwise (ccw).

This distinct feature of this method is that you make a full circle, from 1 to 2 to 3 to 1, completely ignoring the lowest priority group.

3a. If the lowest priority group is behind the steering wheel, then this is the standard orientation: clockwise is R and counter-clockwise is S. (Turning the steering wheel clockwise turns the car to the right-R).

Note that Fischer projections are best depicted as bow ties with horizontal groups coming out and vertical groups back from the central carbon atom.

3b. If the lowest priority group is in front of this curved arrow, then the assignment is reversed: clockwise is S and counterclockwise is R. (Basically, you are looking at the steering wheel from the perspective of the engine compartment!)

Conclusion

The stereochemical configuration of a carbon atom can be specified as either R (rectus) or S (sinister) by using the Cahn-Ingold-Prelog sequence rules. First assign priorities to the four substituents on the chiral carbon atom, and then orient the molecule so that the lowest-priority group points directly back. If a curved arrow drawn in the direction of decreasing priority (1 → 2 → 3) for the remaining three groups is clockwise, the chirality center has the R configuration. If the direction is counterclockwise, the chirality center has the S configuration.

Interpretation Introduction

b)

Interpretation:

R and S configuration is to be assigned to the following molecules.

Concept introduction:

Rule 1:

a) Higher atomic number precedes lower.

b) An atom node duplicated closer to the root ranks higher than one duplicated further.

Rule 2: Higher atomic mass number precedes lower.

Rule 3: Z precedes E and this precedes nonstereogenic (nst) double bonds.

Rule 4:

a) Chiral stereogenic units precede pseudoasymmetric stereogenic units and these precede nonstereogenic units (R = S > r = s > nst).

b) When two ligards have different descriptor pairs, the one with the first chosen like descriptor pairs has priority over the one with a corresponding unlike descriptor pairs.

c) r precedes s.

Rule 5: An atom or group with descriptor R has priority over its enantiomorph S.

Answer to Problem 43AP

S configuration

Explanation of Solution

By ranking the substituent in the following examples based on Cahn-Ingold Prelog rules,

R and S configuration can be assigned to the following molecules.

1. Determine the priorities of the four attached groups from highest (1) to lowest (4).

This is the same as in all methods.

2. Draw the steering wheel. Draw a curved arrow around from 1 to 2 to 3 and back to 1 and note which direction this arrow goes, clockwise (cw) or counterclockwise (ccw).

This distinct feature of this method is that you make a full circle, from 1 to 2 to 3 to 1, completely ignoring the lowest priority group.

3a. If the lowest priority group is behind the steering wheel, then this is the standard orientation: clockwise is R and counter-clockwise is S. (Turning the steering wheel clockwise turns the car to the right-R).

Note that Fischer projections are best depicted as bow ties with horizontal groups coming out and vertical groups back from the central carbon atom.

3b. If the lowest priority group is in front of this curved arrow, then the assignment is reversed: clockwise is S and counterclockwise is R. (Basically, you are looking at the steering wheel from the perspective of the engine compartment!)

Conclusion

The stereochemical configuration of a carbon atom can be specified as either R (rectus) or S (sinister) by using the Cahn-Ingold-Prelog sequence rules. First assign priorities to the four substituents on the chiral carbon atom, and then orient the molecule so that the lowest-priority group points directly back. If a curved arrow drawn in the direction of decreasing priority (1 → 2 → 3) for the remaining three groups is clockwise, the chirality center has the R configuration. If the direction is counterclockwise, the chirality center has the S configuration.

Interpretation Introduction

c)

Interpretation:

R and S configuration is to be assigned to the following molecules.

Concept introduction:

Rule 1:

a) Higher atomic number precedes lower.

b) An atom node duplicated closer to the root ranks higher than one duplicated further.

Rule 2: Higher atomic mass number precedes lower.

Rule 3: Z precedes E and this precedes nonstereogenic (nst) double bonds.

Rule 4:

a) Chiral stereogenic units precede pseudoasymmetric stereogenic units and these precede nonstereogenic units (R = S > r = s > nst).

b) When two ligards have different descriptor pairs, the one with the first chosen like descriptor pairs has priority over the one with a corresponding unlike descriptor pairs.

c) r precedes s.

Rule 5: An atom or group with descriptor R has priority over its enantiomorph S.

Answer to Problem 43AP

S configuration

Explanation of Solution

By ranking the substituent in the following examples based on Cahn-Ingold Prelog rules,

R and S configuration can be assigned to the following molecules.

1. Determine the priorities of the four attached groups from highest (1) to lowest (4).

This is the same as in all methods.

2. Draw the steering wheel. Draw a curved arrow around from 1 to 2 to 3 and back to 1 and note which direction this arrow goes, clockwise (cw) or counterclockwise (ccw).

This distinct feature of this method is that you make a full circle, from 1 to 2 to 3 to 1, completely ignoring the lowest priority group.

3a. If the lowest priority group is behind the steering wheel, then this is the standard orientation: clockwise is R and counter-clockwise is S. (Turning the steering wheel clockwise turns the car to the right-R).

Note that Fischer projections are best depicted as bow ties with horizontal groups coming out and vertical groups back from the central carbon atom.

3b. If the lowest priority group is in front of this curved arrow, then the assignment is reversed: clockwise is S and counterclockwise is R. (Basically, you are looking at the steering wheel from the perspective of the engine compartment!)

Conclusion

The stereochemical configuration of a carbon atom can be specified as either R (rectus) or S (sinister) by using the Cahn-Ingold-Prelog sequence rules. First assign priorities to the four substituents on the chiral carbon atom, and then orient the molecule so that the lowest-priority group points directly back. If a curved arrow drawn in the direction of decreasing priority (1 → 2 → 3) for the remaining three groups is clockwise, the chirality center has the R configuration. If the direction is counterclockwise, the chirality center has the S configuration.