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L-D Configurations: Threose and Erythrose [Question Corrected]
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Mark Timko
L-D Configurations: Threose and Erythrose [Question Corrected]
Your questions is a little unclear, do you mean:
For threose, why is "left, right" D and and "right, left" L (rather than the other way around)?
If this is the question, the answer is that the D/L descriptor is assigned on the basis of the configuration of the last stereocentre (the stereocentre closest to the bottom of the Fisher projection). In the case of erythrose/threose, this is C3. For a pentose, you would assign D/L based on C4, for a hexose C5 and so on.
If the last stereocentre points right in the Fisher projection, it's a D-sugar, if it points left, it's an L-sugar. It doesn't matter what the other OHs are doing, only the last stereocentre is used to assign D/L. This is simply the definition of D/L, it is an arbitrary (but consistent) convention.
For threose, why is "left, right" D and and "right, left" L (rather than the other way around)?
If this is the question, the answer is that the D/L descriptor is assigned on the basis of the configuration of the last stereocentre (the stereocentre closest to the bottom of the Fisher projection). In the case of erythrose/threose, this is C3. For a pentose, you would assign D/L based on C4, for a hexose C5 and so on.
If the last stereocentre points right in the Fisher projection, it's a D-sugar, if it points left, it's an L-sugar. It doesn't matter what the other OHs are doing, only the last stereocentre is used to assign D/L. This is simply the definition of D/L, it is an arbitrary (but consistent) convention.
I meant that the position of the -OH facing to the left on both C2 and C3 like in the Fischer projection for L-Erythrose (and both to the right for D-Erythrose) whereas C2 OH is on the opposite side of C3 OH for the other.
I don't understand the question. Both pointing in the same direction in the Fischer projection is called erythro and pointing opposite directions is called threo - that is just the definition of the erythro/threo stereodescriptors.
I meant that the position of the -OH facing to the left on both C2 and C3 like in the Fischer projection for L-Erythrose (and both to the right for D-Erythrose) whereas C2 OH is on the opposite side of C3 OH for the other.
I don't understand the question. Both pointing in the same direction in the Fischer projection is called erythro and pointing opposite directions is called threo - that is just the definition of the erythro/threo stereodescriptors.
For threose, why is "left, right" D and and "right, left" L (rather than the other way around)?
If this is the question, the answer is that the D/L descriptor is assigned on the basis of the configuration of the last stereocentre (the stereocentre closest to the bottom of the Fisher projection). In the case of erythrose/threose, this is C3. For a pentose, you would assign D/L based on C4, for a hexose C5 and so on.
If the last stereocentre points right in the Fisher projection, it's a D-sugar, if it points left, it's an L-sugar. It doesn't matter what the other OHs are doing, only the last stereocentre is used to assign D/L. This is simply the definition of D/L, it is an arbitrary (but consistent) convention.
For threose, why is "left, right" D and and "right, left" L (rather than the other way around)?
If this is the question, the answer is that the D/L descriptor is assigned on the basis of the configuration of the last stereocentre (the stereocentre closest to the bottom of the Fisher projection). In the case of erythrose/threose, this is C3. For a pentose, you would assign D/L based on C4, for a hexose C5 and so on.
If the last stereocentre points right in the Fisher projection, it's a D-sugar, if it points left, it's an L-sugar. It doesn't matter what the other OHs are doing, only the last stereocentre is used to assign D/L. This is simply the definition of D/L, it is an arbitrary (but consistent) convention.
Remember that L-erythrose and D-erythrose are enantiomers, meaning that they are mirror images. Thus, the stereochemistry at every single stereocenter will be flipped. If you flip the configuration only at one sterocenter, you get a different molecule, not an enantiomer.
Remember that L-erythrose and D-erythrose are enantiomers, meaning that they are mirror images. Thus, the stereochemistry at every single stereocenter will be flipped. If you flip the configuration only at one sterocenter, you get a different molecule, not an enantiomer.
For threose, why is "left, right" D and and "right, left" L (rather than the other way around)?
If this is the question, the answer is that the D/L descriptor is assigned on the basis of the configuration of the last stereocentre (the stereocentre closest to the bottom of the Fisher projection). In the case of erythrose/threose, this is C3. For a pentose, you would assign D/L based on C4, for a hexose C5 and so on.
If the last stereocentre points right in the Fisher projection, it's a D-sugar, if it points left, it's an L-sugar. It doesn't matter what the other OHs are doing, only the last stereocentre is used to assign D/L. This is simply the definition of D/L, it is an arbitrary (but consistent) convention.
Thank you for your reply Dan. The position of the -OH facing to the left on both C2 and C3, like in the Fischer projection, for L-Erythrose (and both to the right for D-Erythrose) whereas C2 OH is on the opposite side of C3 OH for the other.
For threose, why is "left, right" D and and "right, left" L (rather than the other way around)?
If this is the question, the answer is that the D/L descriptor is assigned on the basis of the configuration of the last stereocentre (the stereocentre closest to the bottom of the Fisher projection). In the case of erythrose/threose, this is C3. For a pentose, you would assign D/L based on C4, for a hexose C5 and so on.
If the last stereocentre points right in the Fisher projection, it's a D-sugar, if it points left, it's an L-sugar. It doesn't matter what the other OHs are doing, only the last stereocentre is used to assign D/L. This is simply the definition of D/L, it is an arbitrary (but consistent) convention.
Thank you for your reply Dan. The position of the -OH facing to the left on both C2 and C3, like in the Fischer projection, for L-Erythrose (and both to the right for D-Erythrose) whereas C2 OH is on the opposite side of C3 OH for the other.
Remember that L-erythrose and D-erythrose are enantiomers, meaning that they are mirror images. Thus, the stereochemistry at every single stereocenter will be flipped. If you flip the configuration only at one sterocenter, you get a different molecule, not an enantiomer.
Remember that L-erythrose and D-erythrose are enantiomers, meaning that they are mirror images. Thus, the stereochemistry at every single stereocenter will be flipped. If you flip the configuration only at one sterocenter, you get a different molecule, not an enantiomer.
Remember that L-erythrose and D-erythrose are enantiomers, meaning that they are mirror images. Thus, the stereochemistry at every single stereocenter will be flipped. If you flip the configuration only at one sterocenter, you get a different molecule, not an enantiomer.
Remember that L-erythrose and D-erythrose are enantiomers, meaning that they are mirror images. Thus, the stereochemistry at every single stereocenter will be flipped. If you flip the configuration only at one sterocenter, you get a different molecule, not an enantiomer.
I meant that the position of the -OH facing to the left on both C2 and C3 like in the Fischer projection for L-Erythrose (and both to the right for D-Erythrose) whereas C2 OH is on the opposite side of C3 OH for the other.
I don't understand the question. Both pointing in the same direction in the Fischer projection is called erythro and pointing opposite directions is called threo - that is just the definition of the erythro/threo stereodescriptors.
I meant that the position of the -OH facing to the left on both C2 and C3 like in the Fischer projection for L-Erythrose (and both to the right for D-Erythrose) whereas C2 OH is on the opposite side of C3 OH for the other.
I don't understand the question. Both pointing in the same direction in the Fischer projection is called erythro and pointing opposite directions is called threo - that is just the definition of the erythro/threo stereodescriptors.
For threose, why is "left, right" D and and "right, left" L (rather than the other way around)?
If this is the question, the answer is that the D/L descriptor is assigned on the basis of the configuration of the last stereocentre (the stereocentre closest to the bottom of the Fisher projection). In the case of erythrose/threose, this is C3. For a pentose, you would assign D/L based on C4, for a hexose C5 and so on.
If the last stereocentre points right in the Fisher projection, it's a D-sugar, if it points left, it's an L-sugar. It doesn't matter what the other OHs are doing, only the last stereocentre is used to assign D/L. This is simply the definition of D/L, it is an arbitrary (but consistent) convention.
Thank you for your reply Dan. The position of the -OH facing to the left on both C2 and C3, like in the Fischer projection, for L-Erythrose (and both to the right for D-Erythrose) whereas C2 OH is on the opposite side of C3 OH for the other.
For threose, why is "left, right" D and and "right, left" L (rather than the other way around)?
If this is the question, the answer is that the D/L descriptor is assigned on the basis of the configuration of the last stereocentre (the stereocentre closest to the bottom of the Fisher projection). In the case of erythrose/threose, this is C3. For a pentose, you would assign D/L based on C4, for a hexose C5 and so on.
If the last stereocentre points right in the Fisher projection, it's a D-sugar, if it points left, it's an L-sugar. It doesn't matter what the other OHs are doing, only the last stereocentre is used to assign D/L. This is simply the definition of D/L, it is an arbitrary (but consistent) convention.
Thank you for your reply Dan. The position of the -OH facing to the left on both C2 and C3, like in the Fischer projection, for L-Erythrose (and both to the right for D-Erythrose) whereas C2 OH is on the opposite side of C3 OH for the other.
Remember that L-erythrose and D-erythrose are enantiomers, meaning that they are mirror images. Thus, the stereochemistry at every single stereocenter will be flipped. If you flip the configuration only at one sterocenter, you get a different molecule, not an enantiomer.
Remember that L-erythrose and D-erythrose are enantiomers, meaning that they are mirror images. Thus, the stereochemistry at every single stereocenter will be flipped. If you flip the configuration only at one sterocenter, you get a different molecule, not an enantiomer.
For threose, why is "left, right" D and and "right, left" L (rather than the other way around)?
If this is the question, the answer is that the D/L descriptor is assigned on the basis of the configuration of the last stereocentre (the stereocentre closest to the bottom of the Fisher projection). In the case of erythrose/threose, this is C3. For a pentose, you would assign D/L based on C4, for a hexose C5 and so on.
If the last stereocentre points right in the Fisher projection, it's a D-sugar, if it points left, it's an L-sugar. It doesn't matter what the other OHs are doing, only the last stereocentre is used to assign D/L. This is simply the definition of D/L, it is an arbitrary (but consistent) convention.
For threose, why is "left, right" D and and "right, left" L (rather than the other way around)?
If this is the question, the answer is that the D/L descriptor is assigned on the basis of the configuration of the last stereocentre (the stereocentre closest to the bottom of the Fisher projection). In the case of erythrose/threose, this is C3. For a pentose, you would assign D/L based on C4, for a hexose C5 and so on.
If the last stereocentre points right in the Fisher projection, it's a D-sugar, if it points left, it's an L-sugar. It doesn't matter what the other OHs are doing, only the last stereocentre is used to assign D/L. This is simply the definition of D/L, it is an arbitrary (but consistent) convention.
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I don't understand the question. Both pointing in the same direction in the Fischer projection is called erythro and pointing opposite directions is called threo - that is just the definition of the erythro/threo stereodescriptors.
I don't understand the question. Both pointing in the same direction in the Fischer projection is called erythro and pointing opposite directions is called threo - that is just the definition of the erythro/threo stereodescriptors.
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VOTE
For threose, why is "left, right" D and and "right, left" L (rather than the other way around)?
If this is the question, the answer is that the D/L descriptor is assigned on the basis of the configuration of the last stereocentre (the stereocentre closest to the bottom of the Fisher projection). In the case of erythrose/threose, this is C3. For a pentose, you would assign D/L based on C4, for a hexose C5 and so on.
If the last stereocentre points right in the Fisher projection, it's a D-sugar, if it points left, it's an L-sugar. It doesn't matter what the other OHs are doing, only the last stereocentre is used to assign D/L. This is simply the definition of D/L, it is an arbitrary (but consistent) convention.
For threose, why is "left, right" D and and "right, left" L (rather than the other way around)?
If this is the question, the answer is that the D/L descriptor is assigned on the basis of the configuration of the last stereocentre (the stereocentre closest to the bottom of the Fisher projection). In the case of erythrose/threose, this is C3. For a pentose, you would assign D/L based on C4, for a hexose C5 and so on.
If the last stereocentre points right in the Fisher projection, it's a D-sugar, if it points left, it's an L-sugar. It doesn't matter what the other OHs are doing, only the last stereocentre is used to assign D/L. This is simply the definition of D/L, it is an arbitrary (but consistent) convention.
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Thank you for your reply Dan. The position of the -OH facing to the left on both C2 and C3, like in the Fischer projection, for L-Erythrose (and both to the right for D-Erythrose) whereas C2 OH is on the opposite side of C3 OH for the other.
Thank you for your reply Dan. The position of the -OH facing to the left on both C2 and C3, like in the Fischer projection, for L-Erythrose (and both to the right for D-Erythrose) whereas C2 OH is on the opposite side of C3 OH for the other.
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I don't understand the question. Both pointing in the same direction in the Fischer projection is called erythro and pointing opposite directions is called threo - that is just the definition of the erythro/threo stereodescriptors.
I don't understand the question. Both pointing in the same direction in the Fischer projection is called erythro and pointing opposite directions is called threo - that is just the definition of the erythro/threo stereodescriptors.
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Thank you for your reply Dan. The position of the -OH facing to the left on both C2 and C3, like in the Fischer projection, for L-Erythrose (and both to the right for D-Erythrose) whereas C2 OH is on the opposite side of C3 OH for the other.
Thank you for your reply Dan. The position of the -OH facing to the left on both C2 and C3, like in the Fischer projection, for L-Erythrose (and both to the right for D-Erythrose) whereas C2 OH is on the opposite side of C3 OH for the other.
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