A functional group characterized by a hydroxyl (-OH) group bonded to an sp3 hybridized carbon atom, typically part of an alkyl chain or cycloalkane ring.
This distinguishes it from a phenol, where the hydroxyl group is directly attached to an aromatic ring, leading to different chemical properties.
Card 2
Aldehyde
Answer
A functional group containing a carbonyl (C=O) group bonded to at least one hydrogen atom and one alkyl or aryl group (or two hydrogen atoms in formaldehyde).
The presence of at least one hydrogen directly attached to the carbonyl carbon is the key feature that differentiates aldehydes from ketones.
Card 3
Ketone
Answer
A functional group characterized by a carbonyl (C=O) group bonded to two alkyl or aryl groups.
Unlike aldehydes, ketones do not have a hydrogen atom directly attached to the carbonyl carbon, which affects their reactivity in oxidation reactions.
Card 4
Carboxylic Acid
Answer
A functional group containing a carboxyl group (-COOH), which consists of a carbonyl group bonded to a hydroxyl group.
Carboxylic acids are typically weak acids due to the resonance stabilization of their conjugate base, the carboxylate ion.
Card 5
Ester
Answer
A functional group derived from a carboxylic acid where the hydrogen of the carboxyl's hydroxyl group is replaced by an alkyl or aryl group (-COOR').
Esters are often responsible for the pleasant fragrances of fruits and flowers, and they are less acidic than carboxylic acids.
Card 6
Amine
Answer
A functional group characterized by a nitrogen atom bonded to one, two, or three alkyl or aryl groups, and potentially one or two hydrogen atoms.
Amines are typically basic due to the lone pair of electrons on the nitrogen atom, distinguishing them from amides where nitrogen is adjacent to a carbonyl.
Card 7
IUPAC Nomenclature
Answer
A systematic method for naming chemical compounds established by the International Union of Pure and Applied Chemistry, ensuring each unique structure has a unique, unambiguous name.
Following IUPAC rules is crucial for clear communication among chemists, avoiding confusion that can arise from common or trivial names.
Card 8
Prefix (Nomenclature)
Answer
A part of an IUPAC name that indicates the number of carbon atoms in a parent chain (e.g., 'meth-', 'eth-') or the identity and position of substituents (e.g., 'methyl', 'chloro').
Prefixes describe 'what' and 'where' a substituent is, while the root indicates the main carbon chain length.
Card 9
Suffix (Nomenclature)
Answer
A part of an IUPAC name that indicates the primary functional group present in the molecule, dictating the compound's class (e.g., '-ol' for alcohol, '-al' for aldehyde, '-oic acid' for carboxylic acid).
The suffix is determined by the highest priority functional group and is typically placed at the end of the parent chain name.
Card 10
R/S Configuration
Answer
A system used to describe the absolute configuration of a chiral center, determined by assigning priorities to its four different substituents and observing their spatial arrangement.
This system provides an unambiguous way to differentiate between enantiomers, which are non-superimposable mirror images.
Card 11
Chiral Center
Answer
A carbon atom bonded to four different groups, making the molecule non-superimposable on its mirror image and thus chiral.
The presence of a chiral center is the most common reason for a molecule to exhibit chirality, though not the only one (e.g., allenes can be chiral without chiral centers).
Card 12
Enantiomers
Answer
Stereoisomers that are non-superimposable mirror images of each other, possessing identical physical properties except for their interaction with plane-polarized light and their reactivity in chiral environments.
A common mistake is confusing enantiomers with identical molecules; they are distinct isomers even though they are mirror images.
Card 13
Diastereomers
Answer
Stereoisomers that are not mirror images of each other, typically arising from compounds with two or more chiral centers.
Unlike enantiomers, diastereomers have different physical and chemical properties, such as melting points, boiling points, and solubilities.
Card 14
Meso Compound
Answer
An achiral compound that contains two or more chiral centers, possessing an internal plane of symmetry or a center of inversion that makes the molecule superimposable on its mirror image.
Meso compounds are optically inactive despite having chiral centers, often a point of confusion for students learning stereochemistry.
Card 15
Racemic Mixture
Answer
A 1:1 mixture of two enantiomers, resulting in a solution that is optically inactive because the rotations of plane-polarized light by the two enantiomers cancel each other out.
Racemic mixtures are often formed in reactions that produce a new chiral center from an achiral starting material without a chiral catalyst.
Card 16
Optical Activity
Answer
The ability of a chiral substance to rotate the plane of plane-polarized light, measured by a polarimeter.
Enantiomers rotate plane-polarized light to an equal extent but in opposite directions, one being dextrorotatory (+) and the other levorotatory (-).
Card 17
E/Z Configuration
Answer
A system used to describe the relative stereochemistry of substituents on a double bond, based on atomic number priority rules.
E (entgegen, opposite) indicates higher priority groups are on opposite sides of the double bond, while Z (zusammen, together) indicates they are on the same side.
Card 18
Conformational Isomers (Conformers)
Answer
Stereoisomers that can be interconverted by rotation around single bonds, without breaking or forming any covalent bonds.
Unlike configurational isomers (like enantiomers or diastereomers), conformers are generally not isolable at room temperature due to rapid interconversion.
Card 19
Resonance Structures (Canonical Forms)
Answer
Hypothetical Lewis structures that represent the delocalization of electrons within a molecule or ion where a single Lewis structure is insufficient to describe the bonding accurately.
It's crucial to remember that resonance structures are not in equilibrium; the true structure is a hybrid of all valid contributors.
Card 20
Resonance Hybrid
Answer
The actual structure of a molecule or ion that is an average or blend of all its valid resonance structures, more stable than any single contributing structure.
The resonance hybrid depicts the delocalization of electrons as partial bonds and partial charges, representing the molecule's true electron distribution.
Card 21
Electron Delocalization
Answer
The spreading of electron density over a larger area than a single bond or atom, typically involving pi electrons or lone pairs, which enhances molecular stability.
Delocalization lowers the potential energy of the molecule, making it more stable than if the electrons were localized to specific bonds or atoms.
Card 22
Major Resonance Contributor
Answer
A resonance structure that contributes more significantly to the overall resonance hybrid than others due to factors such as having more covalent bonds, fewer formal charges, or negative charges on more electronegative atoms.
Identifying the major contributor helps predict the actual electron distribution and reactivity of a resonance-stabilized species.
Card 23
SN1 Mechanism
Answer
A two-step nucleophilic substitution reaction involving a carbocation intermediate, where the rate-determining step is the formation of the carbocation.
SN1 reactions typically favor tertiary alkyl halides and weak nucleophiles, often resulting in a racemic mixture if the carbocation is planar.
Card 24
SN2 Mechanism
Answer
A concerted, one-step nucleophilic substitution reaction where the nucleophile attacks and the leaving group departs simultaneously, resulting in inversion of configuration at the reacting carbon.
SN2 reactions favor primary alkyl halides and strong nucleophiles, and are sensitive to steric hindrance at the reaction center.
Card 25
Nucleophile
Answer
An electron-rich species that donates a pair of electrons to form a new covalent bond with an electron-deficient center (an electrophile).
Nucleophiles are often negatively charged (e.g., OH-) or possess lone pairs of electrons (e.g., H2O, NH3).
Card 26
Leaving Group
Answer
An atom or group of atoms that departs with its bonding electrons during a substitution or elimination reaction, forming a stable anion or neutral molecule.
Good leaving groups are typically weak bases, as their conjugate acids are strong (e.g., halides, tosylates).
Card 27
E1 Mechanism
Answer
A two-step elimination reaction involving a carbocation intermediate, typically forming the more substituted alkene (Zaitsev product) and competing with the SN1 reaction.
Like SN1, E1 reactions favor tertiary alkyl halides and are often carried out with weak bases in protic solvents.
Card 28
E2 Mechanism
Answer
A concerted, one-step elimination reaction where a strong base removes a proton and the leaving group departs simultaneously, requiring an anti-periplanar arrangement of the leaving group and the proton.
E2 reactions are stereospecific and regioselective, typically yielding the Zaitsev product unless bulky bases are used.
Card 29
Zaitsev's Rule
Answer
In an elimination reaction, the major product is typically the most substituted alkene, meaning the alkene with the greatest number of alkyl groups attached to the double-bond carbons.
This rule predicts the regioselectivity of many elimination reactions, favoring the more stable alkene product.
Card 30
Anti-periplanar Geometry
Answer
The required spatial arrangement for an E2 elimination reaction where the leaving group and the proton on the adjacent carbon are in the same plane but on opposite sides, allowing for optimal orbital overlap in the transition state.
This specific geometry is crucial for the concerted mechanism of E2, facilitating the simultaneous bond breaking and formation.