Ochem Flashcards
Hybridization
-a way of making all of the bonds to a central atom equivalent to each other
-sp3 = tetrahedral (hallmark of carbon containing molecules, one s and 3 p-orbitals)
-sp2 = trigonal planar geometry (one s orbital mixed w/ 2 p orbitals , the third p orbital is unhybridized and can be used to form a π bond), seen in alkenes
-sp = linear geometry ( to form a triple bond, 2 of the p orbitals form π bonds and the third p orbital will combine w/ the s orbital to form 2 sp orbitals)
Resonance
describes the delocalization of electrons in molecules that have conjugated bonds (when single and multiple bonds alternate)
Lewis acid
is an electron acceptor in the formation of a covalent bond, tend to be electrophiles
Lewis base
is an electron donor in the formation of a covalent bond, nucleophiles
Brønsted-Lowry acid
species that can donate a proton (H+)
Bronsted-Lowry base
a species that can accept a proton
Amphoteric
molecules like water that have the ability to act as either Bronsted-Lowry acids or bases
Acid dissociation constant, Ka
measures the strength of an acid in solution
Ka = [HA+][A-]/[HA]
pKa of acid
pKa = -logKa
Nucleophiles
“nucleus-loving” species with either lone pairs or π bonds that can form new bonds to electrophiles
–good nucleophiles tend to be good bases
In protic solvents, nucleophilicity decreases in the order
I- > Br- >Cl- > F-
In aprotic solvents, nucleophilicity decreases in the order
F- > Cl- > Br- > I-
Electrophiles
“electron-loving” species with a positive charge or positively polarized atom that accepts an electron pair when forming new bonds with a nucleophile
Leaving groups
the molecular fragments that retain the electrons after heterolysis
-weak bases make good leaving groups (I-, Br-, and Cli)
SN1 reaction
-contains two steps, the first step is the rate-limiting step
-1. the leaving group leaves, generating a positively charged carbocation. 2. The nucleophile attacks the carbocation, resulting in the substitution product
-the rate of the reaction only depends on the concentration of the substrate: rate = k[R-L]
-first order reaction; anything that accelerates the formation of the carbocation will increase the rate of this rxn
-product will usually be a racemic mixture
SN2 reaction
-contains only one step in which the nucleophile attacks the compound at the same time as the leaving group leaves
-concerted reaction
-the single rate-limiting step involves 2 molecules (the substrate & the nucleophile)
-the concentrations of the substrate and the nucleophile have a role in determining the rate: rate = k[Nu][R - L]
-the nucleophile actively displaces the leaving group in a backside attack
Nomenclature of Alcohols
-have the general formula ROH, with the functional group -OH referred to as a hydroxyl group
-names in the IUPAC by replacing the -e ending of the root alkane w/ -ol
-common naming practice is to name the alkyl group as a derivative followed by alcohol
-when the alcohol is not the highest-priority group, it is named as a substituent w/ the prefix hydroxy-
Phenols
-hydroxyl groups that can be attached to aromatic rings
-the hydroxyl hydrogens are acidic due to resonance within the phenol ring
-have higher melting and boiling points than other alcohols due to intermolecular hydrogen bonds
-more acidic than nonaromatic alcohol, so they can form salts w/ inorganic bases such as NaOH
-Ortho: two groups on adjacent carbons
-Meta: two groups separated by a carbon
-Para: two groups on opposite sides of the ring
Oxidation reactions of alcohols
-Primary alcohols can be oxidized to aldehydes, but only by pyridinium chlorochromate (PCC)— oxidation of primary alcohols w/ a strong oxidant like chromium (VI) will produce a carboxylic acid
-Secondary alcohols can be oxidized to ketones by PCC or any stronger oxidizing agent —- oxidation w/ a strong oxidizing agent can fully oxidize secondary alcohols to ketones
-Tertiary alcohols cannot be oxidized because they are already as oxidized as they can be w/o breaking a carbon-carbon bond
-Jones oxidation (CrO3 dissolved w/ dilute sulfuric acid in acetone) oxidizes primary alcohols to carboxylic acids and secondary alcohols to ketones
Reactions of Phenols (quinones and hydroxyquinones)
-treatment of phenols w/ oxidizing agents produces compounds called quinones –named by indicating the position of the carbonyls numerically and adding quinone to the name of the parent phenol —some do have aromatic rings but not always, serve as electron acceptors biochemically, specifically in the electron transport chain in both photosynthesis and aerobic respiration
-hydroxyquinones share the same ring and carbonyl backbone as quinones, but differ by the addition of one or more hydroxyl groups, many have biological activity and are used in the synthesis of medications
Reactions of Phenols (ubiquinone)
-an example of a biologically active quinone, also called coenzyme Q and is a vital electron carrier associated w/ complexes I, II, and III of the ETC
-the most oxidized form that this molecule takes physiologically: it can also be reduced to ubiquinol upon the acceptance of electrons —-this oxidation-reduction capacity allows the molecule to perform its physiological function of the electron transport
Tautomerization
movement of a hydrogen and a double bond
Micheal addition
the addition of an enolate to an electrophilic alkene, such as an α-β unsaturated ketone, nitrile, or ester
Imine
a compound that contains a C-N double bond
Aldol condensation
an aldehyde or ketone acts both as an electrophile (in its keto form) and a nucleophile (in its enolate form), and the end result is the formation of a carbon-carbon bond — product is an aldol (a molecule that contains both aldehyde and alcohol functional groups)
Carboxylic acids
contain both a carbonyl group and a hydroxyl group, bonded to the same carbon
-one of the most oxidized fg
-are always terminal groups
Nucleophilic acyl substitution (carboxylic acids)
after opening the carbonyl via nucleophilic attack and forming a tetrahedral intermediate, the carbonyl can reform, thereby kicking off the leaving group
1. Nucleophilic addition
2. Elimination of the leaving group and reforming of the carbonyl
–*weak bases make good leaving groups
Esterification
a condensation reaction with water as a side product
-in acidic solutions, the carbonyl oxygen can be protonated, which enhances the polarity of the bond, thereby placing additional positive charge on the carbonyl carbon and increasing its susceptibility to nucleophilic attack
-occurs most rapidly with primary alcohols
Anhydrides
can be formed by the condensation of two carboxylic acids
-named by replacing the acid at the end of the name of the parent carboxylic acid with anhydride, whether cyclic or linear
-forms via nucleophilic acyl substitution
Reduction of carboxylic acids
-carboxylic acids can be reduced to primary alcohols by the use of lithium aluminum hydride (LiAlH4)
-aldehyde intermediates may be formed in the course of this reaction, but they, too, will be reduced to the alcohol
-the reaction occurs by nucleophilic addition of hydride to the carbonyl group
-a gentler reducing agent like sodium borohydride (NaBH4) is not strong enough to reduce carboxylic acids
Saponification
-when long-chain carboxylic acids react with sodium or potassium hydroxide, a salt is formed
-occurs by mixing fatty acids with lye (sodium or potassium hydroxide), resulting in the formation of a salt that we know as soap
Amides
-carboxylic acid derivative
-generally synthesized by the rxn of other carboxylic acid derivatives w/ either ammonia or an amine
–only primary and secondary amines undergo this reaction
-cyclic amides= lactams
Esters
-the dehydration synthesis products of other carboxylic acid derivatives and alcohols
-rxn is called a Fischer esterification, can also be obtained from the rxn of anhydrides w/alcohols
-cyclic esters = lactones
–lack hydrogen bonding, so they have lower boiling points than their related carboxylic acids
Anhydrides
also called acid anhydrides, are the condensation dimers of carboxylic acids
Characteristic IR absorptions
-hydroxyl group: broad wide peak at 3300 cm^-1 for alcohols and 3000 cm^-1 for carboxylic acids
-carbonyl: sharp deep peak at 1700 cm^-1
-N-H bonds: in the same regions O-H bonds (around 3300 cm^-1, but have a sharp peak instead of a broad one)
