Organic Chemistry Flashcards
Which of the following is true about the structure and reactivity of steroids.
I. Steroids contain only three fused hydrocarbon rings
II. Steroids are made of two isoprene units
III. Steroids are nonhydrolyzable lipids
III only
Steroids are made up of triterpenes, three monoterpenes, or six isoprene units, which are synthesized by the cyclization of the triterpene squalene, forming cholesterol. Cholesterol itself contains four fused hydrocarbon rings.
Diastereomers, enantiomers, and conformational isomers
are stereoisomers with the same connectivity but different spatial orientation
structural isomers
differ in how the atoms are connected at one or more points within the structure
Which of the following is true regarding the relative stability of carbocation and carbanion species species as the number of alkyl substituents increases relative to hydride substituents?
A) As the number of alkyl substituents increases, carbocation stability increases but carbanion stability decreases
B) As the number of alkyl substituents increases, carbocation stability decreases but carbanion stability increases
C) As the number of alkyl substituents increases, carbocation stability and carbanion stability both increase
D) As the number of alkyl substituents increases, carbocation stability and carbanion stability both decrease
A) As the number of alkyl substituents increases, carbocation stability increases but carbanion stability decreases
Carbocations, molecules containing a positively charged carbon atom, are strong electrophiles and a common intermediate in Sn1 and E1 reactions. Carbanions, which contain a negatively charged carbon atom, act as strong nucleophiles due to the lone pair of electrons on the charged carbon.
Because nearby alkyl groups are electron donating, they help stabilize carbocations (make them less reactive) but destabilize carbanions (make them more reactive)
Therefore: The order of decreasing stability for these species is:
Carbocation: tertiary > secondary > primary > methyl
Carbanion: methyl > primary > secondary > tertiary
Structure of the substrate for the reaction catalyzed by glutamate racemase?
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The reaction catalyzed by glutamate racemase produces D-glutamate from its substrate L-glutamate, which has an S absolute configuration. Therefore, the correct answer should show glutamate with an S congifuration at the a-carbon.
To determine R/S configurion:
- Assign priority to each a-carbon substituent. Higher priority is given to atoms with greater atomic number. In case of a tie, the atomic weights of the next attached atoms are considered.
- If the lowest priority group points behind the plan, a clockwise arrangement of the other three substituents corresponds to an R configuration, and a counterclockwise arrangement corresponds to an S configuration. If the lowest priority group points in front of the plane (wedged bond), the opposite is true
The side chain of glutamate, also known as glutamic acid (Glu, E), consists of two straight-chain carbon atoms bonded to a carboxylic acid. The structure in choice B shows L-glutamate, which has an S-configuration at the a-carbon
Imine
Structure containing a carbon-nitrogen double bond C=N
During conversion of an amino acid from the L to the D configuration in a PLP-dependent enzyme, a base removes a proton from the a-carbon. Reprotonation of the resulting planar molecule involves the nucleophilic attack of a proton donor:
A) in a nonstereospecific manner
B) on either side of the planar intermediate with equal likelihood
C) with an orientation opposite that of the proton that was removed
D) with the same orientation as the proton that was removed
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C) with an orientation opposite that of the proton that was removed
The racemase-catalyzed conversion of L-glutamate to D-glutamate is stereospecific. The planar intermediate (imine) in formed in step 3 of the PLP-dependent reactions (Figure 2) after hydrogen is removed from the chiral carbon atom in L-glutamate. In step 4, the enzyme catalyzes the addition of hydrogen to the opposite side, which allows for the conversion to D-glutamate.
Ethylhexyl glycerin could be most efficiently synthesized from glycerol and which of the following? (which leaving group)
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I leaving group on end
Sn2 reactions occur when a nucleophile donates electrons to an electrophile with a good leaving group. The halogens are generally good leaving groups because they can form stable anions. Larger halogens are better leaving groups than small halogens because they can spread the negative charge over a larger surface area.
Why does the bond between glycerol and the ethylhexyl group tend to form at glycerol’s C1 hydroxyl group instead of the C2 hydroxyl group?
A) Secondary alcohols are more likely to undergo Sn1 reactions than primary alcohols
B) Secondary alcohols are more sterically hindered than primary alcohols
C) Primary alcohols are less acidic than secondary alcohols
D) primary alcohols are more electrophilic than secondary alcohols
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B) Secondary alcohols are more sterically hindered than primary alcohols
Acid helps catalyze the Fischer estification reaction by doing all of the following except:
A) enhancing the nucleophilicity of alcohols
B) forming a stable carbocation intermediate
C) creating a good leaving group
D) increasing carbonyl electrophilicity
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A) enhancing the nucleophilicity of alcohols
Acid-catalyzed reactions generally do not increase the nucleophilicity of anything because nucleophiles are attracted to positive charge. Acids increase the positive charge of molecules, making them less attracted to other positive charges and less nucleophilic.
By approximately what factor were the bacteria recovered from hands reduced when hands were washed with 3.0 mL of soap vs no soap?
-reading log graph
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100
0 ml, 6 log (10^6)
3 ml, 4 log (10 ^4)
10^6 - 10^4 = 100
