PCAT Organic Chemistry – Flashcards
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Hybridization, geometry, and bonding characteristics of Carbon
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-carbon always obeys the octet rule in neutral molecules -sp3: tetrahedral; 109.5; 4 single covalent bonds around C -sp2: trigonal planar; 120; 1 double and two single bonds around C -sp: linear; 180; either one triple and one single, or 2 double
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Carbon ions may or may not obey the octet rule
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sp3: tetrahedral;109.5; obeys octet rule -sp2: trigonal planar; 120; does not obey octet rule -sp: linear;N/A; obeys octet rule
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Hybridization, geometry, and bonding characteristics of Nitrogen and Oxygen
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-like carbon, nitrogen and oxygen obey the octet rule in neutral molecules -unlike carbon, they complete their octet with lone pairs of electrons -therfore, their electronic geometry is different from their molecular geometry
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Nitrogen and Oxygen hybridizations
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-sp3: tetrahedral electronic geometry;bent or pyramidal molecular geometry -sp2: trigonal planar electronic geometry; linear or bent molecular geometry -sp: linear electronic and molecular geometry
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Molecular shape and polarity
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-molecules that have sp or sp2 hybridized atoms only (other than H) will generally be flat (two dimensional) -the shape of the molecule (in addition to the polarity of individual bonds) determines many of its physical properties -more symmetric/less polar molecules will have lower boiling points -melting points may or may not follow this rule, as more symmetrical molecules typically pack better (more tightly), requiring more energy to melt the solid -when comparing cis and trans alkenes, the more symmetrical/less polar trans alkene has lower bp and higher mp than cis
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Bond length
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-the more s character an orbital has, the shorter the bond it makes is -therefore, the length of the bonds shown below increases L to R -H-H (s-s)< C=-C (sp-sp) < C=C (sp2-sp2) < C-C (sp3-sp3)
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Elements of unsaturation
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-the general formula for an alkane is CnH2n+2 -compounds with double bonds, triple bonds, or rings have less than 2n+2 Hs relative to the number of carbons. it is said that these compounds are unsaturated -each element of unsaturation is 2 Hs less than the max -we compare the formula of a given compound to that of the fully saturated alkane with the same number of Cs, subtract the Hs, and divide the difference by 2. that will tell us the elements of unsaturation -1 double bond or 1 ring= 1 element of unsaturation -1 triple bond= 2 elements of unsaturation
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Sigma and Pi bonds
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-sigma bond: head on overlap of atomic (s,p) or hybrid (sp, spa, spa) orbitals -pi bond: side-to-side overlap of p orbitals -single covalent bonds: 1 sigma, 0 pi -double covalent bonds: 1 sigma, 1 pi -triple covalent bonds: 1 sigma, 2 pi -any atom involved in a double bond has both spy orbitals (to form sigma bonds) and a p orbital ( to form the pi bond) -any atom involved in a triple bond has sp orbitals ( to form sigma bonds) and two p orbitals ( to form 2 pi bonds) -H atoms bond with their unhybridized s orbitals
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Hydrogen bonding
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-attraction between the positive H in one molecule and the negative N, O, or F in another -molecules with -OH or -NH 0r HF can hydrogen bond
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Solubility
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-like dissolves like; polar compounds tend to dissolve polar compounds and non polar dissolve non polar -since organic molecules mostly have C-C or C-H bonds, they tend to dissolve in non polar solvents
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Boiling point
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-when comparing similar molecules, bp increase with increasing number of carbons (increasing mw or mass) -a polar group (more electronegative) will increase the bp of a molecule when compared to a molecule of similar weight with a less polar group -groups that can hydrogen bond will increase the bp the most -compounds with low bps (most organic) have a lot of vapor pressure associated with the liquid or are gases at room temp (this makes them flammable/explosive/combustable)
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Acid/base, nucleophile/electrophile
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-base: bronsted-lowry (proton acceptor) -acid: bronsted-lowry (proton donor) -nucleophile: lewis base (electron donor) -electrophile: lewis acid (electron acceptor) -strong acids ionize readily; this is due to the stability of the conjugate base formed; the stronger the acid, the more stable the conjugate base -conjugate base stability can be due to: 1)higher electronegativity of an atom in the conjugate base (drawing electron density away from the atom with the negative charge) 2)larger size (polarizability- better able to diffuse the neg charge) 3)resonance stabilization (delocalize neg charge) -electronegativity arguments usually apply when comparing atoms in the same row while size arguments tend to compare atoms in a column on the periodic table
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Nomenclature of alkanes and cycloalkanes: alkanes
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-are hydrocarbons that have single C-C covalent bonds only (saturated) -alkanes are named based on the number of carbon atoms in the base chain -we use specific prefixes to indicate the number of carbons (meth=1, eth=2, prop=3, but=4, pent=5, hex=6, hept=7, oct=8, non=9, dec=10) -each C in an alkane must have 4 single covalent bonds -substituents end in -yl (ex. methyl, ethyl)
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Rules for naming branched alkanes
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1) locate the longest chain of consecutive C atoms 2) number the carbons in base chain, with C #1 being closest to the first substituent 3) name first the substituents attached to base chain in alphabetical order 4) use de-, tri-... for multiples of same substituent 5) halogen atoms attached to C are treated as substituents (fluoro-, iodo, cholera, bromo) 6) finish the name with the base chain name
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Cycloalkanes
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-hydrocarbons that have a base ring rather than a base chain -the rules for naming are the same for naming alkanes except that the ring will be numbered to give the lowest possible combination of carbon numbers to substituents
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Functional groups
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-alkane: none -alkene: C=C -alkyne: -C=-C- -nitrile: R-C=-C- -alcohol: R-OH -amines: R-NH2 -ether: R-O-R -imine: 2R-C=NR -aldyhyde: RH-C=O -ketone: 2R-C=O -carboxylic acid: R-COOH -ester: R-CO2-R -amides: NH2-C=O
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Nomenclature of molecules with functional groups
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1) locate the longest chain of consecutive C atoms that contain or is attached to the functional group 2) number the carbons in base chain, with C #1 being closest to the functional group 3) the ending of the base chain name will reflect the nature of the functional group: -ene for alkene, -yne for alkyne, -ol for alcohol, -al for aldehyde, -one for ketone, -oic acid for carboxylic acid, nitrile for nitrile 4) locations of functional groups must be specified 5) if more than one of the same functional groups is present, use di-, tri-... giving location of each 6) if more than one type of functional group is present, the one with highest priority (most oxidized) will be the base chain and others become substituents
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Common names
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-alcohols: name ends in alcohol; name begins with the name of the alkyl group that is attached to the -OH -ketones, ethers, and amines: name the alkyl substituents attached to the C=O, O, or N; use di-, tri- if the alkyl substituents are the same -aldehydes, carboxylic acids, and carboxylic acid derivatives: 1 C= form-; 2 C= acet-; 3 C= propion-; 4 C= butyr-; name ends in aldehyde, -oic acid, -ate (ester), -amide, and -nitrile
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Systemic and common names for carboxylic acid derivatives
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-the -OH in a carboxylic acid can be replaced with -OR, -NH2, or NR2... -name the carboxylic acid first -replace "oic acid" in the carboxylic acid for the ending of each functional group (-ate for ester, -amide for amides...) -before the base chain name, list the alkyl substituents that are attached to the O or N
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Aromatic compounds
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-aromatic compounds are compounds that contain the benzene ring as a base -as with cycloalkanes, we number the carbons in the ring so that the substituents are in lowest possible combinations of carbon numbers -the name will end in -benzene -disubstituted benzene compounds can be named using numbers or ortho, meta, para
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Aromaticity
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-the cyclic compound is more stable than the open chain counterpart; the opposite is true for anti aromatic compounds -cyclic with conjugated pi bonds -each atom in the ring must be sp2 hybridized, with an unhybridized p orbital -the p orbitals must overlap continuously around the ring (planar)
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Huckels rule
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-aromatic: a continuous ring of overlapping p orbitals that has 4N+2 pi electrons -anti-aromatic: a continous ring of overlapping p orbitals that has 4N pi electrons
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Isomers
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-are different molecules that share the same molecular formula
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Structural isomers
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-molecules that have a different bonding sequence
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Stereoisomers
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-molecules that have the same bonding sequence but different spatial orientation -enantiomers: stereoisomers that are non-superimposable mirror images -a molecule with one sp3 C with four different groups attached is said to have a chiral carbon, which will have an enantiomer -when placed in a polarimeter, one enantiomer will rotate the plane of polarized light clockwise while the other enantiomer will rotate it counter-clockwise -a pure sample of each enantiomer is said to be optically active; while a 50/50 mix will not rotate polarized light and is optically inactive (racemic mixture) -diastereomers: stereoisomers that are not mirror images -ex. cis and trans
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Substitution and elimination reactions (pics on pg 23)
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-these are reactions that typically occur when using alkyl halide as a substrate -alkyl halide are molecules where a halogen is connected to an sp3 C -alkyl halide are good substrates for substitution and elimination reactions because halogens are good leaving groups (stable as a negative ion due to large size and high electronegativity)
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Nucleophilic substitution
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-a nuc replaces the leaving group in the alkyl halide
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Elimination
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-both the halide ion and H are lost forth alkyl halide and a new pi bond is formed
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Both nucleophilic substitution and elimination reactions can occur in one or two steps
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-Sn2 and E2 occur in one step; the 2 refers to the 2 reactants- alkyl halide and nuc/base that are involved in the rate determining step -Sn1 and E1 occur in two steps; alkyl halide involved in first rate determining step and nuc/base in second step
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Sn2
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-a strong nuc (OH-) attacks the back side of the electrophilic carbon of alkyl halide, forcing the leaving group (Br-) to leave -concerted, one step reaction (making and breaking bonds occurs simultaneously) -back side attack results in inversion of configuration (R to S or S to R) if the carbon involved is chiral -the nuc must be able to reach the electrophilic sp3 carbon attached to the Br from the back. the smaller the groups attached to C, the easier it will be for the nuc to reach it -the nature of the alkyl halide is one of the factors that determines the rate (fastest) CH3X>1>2>>>3 (unreactive)
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Sn1
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-1st step: formation of carbocation intermediate, rate determining step -2nd step: fast step with subsequent loss of H+ if necessary -the strength of the nuc is unimportant, since it is not involved in the rate determining step; the nuc can also be the solvent (water hydrolysis resulting in an alcohol; alcohol solvolysis resulting in ethers) -two step reaction with the formation of a reactive intermediate: the flat carbocation -racemization occurs -alkyl groups are electron donors. the more alkyl groups attached to the carbocation, the more stable it will be and the faster the reaction will proceed -the rate of reactions relative to alkyl halides is the opposite of Sn2 (fastest) 3>2>>>1 (unreactive)
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E2
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-a strong base (OH-) abstracts a proton from a poor Sn2 substrate (3 alkyl halide- sterically hindered for back side attack by a nuc is best) -concerted, one step reaction -bromide ion leaves as the proton is abstracted -pi bond forms -the order of reactivity for alkyl halides is 3>2>1 -if more than one alkene can form, the more substituted alkene is generally the major product
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E1
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-1st step: formation of carbocation intermediate, rate determining step -2nd step: fast step -the strength of the base in unimportant, since is it not involved in the rate determining step -two step reaction with the formation of a reactive intermediate in the first, rate determining step: the flat carbocation. this first step is the same as Sn1 -the stability of the carbocation determines the rate of reaction -the rate of reaction relative to the alkyl halide is (fastest) 3>2>>>1 (unreactive) -if more than one alkene can form, the more substituted alkene is generally the major product
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Dehydration reactions
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-elimination reactions can occur with substrates other than alkyl halides, as long as there is a good leaving group attached to the sp3 C -in general OH- is a lousy leaving group (strong base, will attack the product formed) but H2O is a good leaving group -thus, alcohols can undergo an elimination reaction if they are protonated first in acid -the net result of the elimination reaction of an alcohol is the loss of water with the formation of an alkene -as with alkyl halides, the rate of reaction relative to the substrate is 3>2>>>1
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Addition reactions to alkenes
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-pi electrons in alkenes are loosely held and nucleophilic -these pi electrons will attack an electrophile and form a carbocation -a nuc (water, bromide ion...) will then add to the carbocation -the net result is addition to the double bond, with the double bond becoming a single bond -many different types of addition reactions to a double bond are possible. one important consideration is the regiochemistry of the product -the Markovnikov product forms when the proton of an acid adds to the carbon in the double bond that already has the most Hs -the anti-Markovnikov product forms when H adds to the more substituted carbon of the double bond -Markovnikov products occur under acidic conditions. the first rate determining step involves protonation with the formation of the more substituted carbocation. addition of the nuc to the carbocation gives rise to the product -formation of non-Markovnikov products is the result of a reaction mechanism that does not involved a carbocation
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Alkene reactions (pics on pg 31)
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-HBr--> Markovnikov -HBr/ROOR--> anti-Markovnikov -H+,H2O--> Markovnikov -1)Hg(Oac)2, HOR 2) NaBH4--> Markovnikov -1)BH3,THF 2)H2O2, OH---> anti-Markovnikov -if rather than adding HX we add X2, there are no regioselectivity issues -addition of halogens to an alkene is possible because of the polarizability of the halogen. as X2 approaches the site of high electron density (double bond), X2 is polarized (electrons shift from one end to the other) such that the nearest X atom now has some partial positive charge. the pi electrons of the double bond attack the positive X atom, breaking the X-X bond. the smaller the molecule, the less polarizable it is (F2 is the least)
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Epoxide opening
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-another way of obtaining 1,2 diols (besides hydroxylation) is by opening an epoxide with water -epoxides are 3 membered rings with two carbons and one oxygen that are obtained by adding O to alkenes (the sources of the O are peroxyacid) -the epoxide can then be opened by water under acidic conditions or with OH- under basic conditions to yield a trans 1,2 diol
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Addition reactions to alkynes
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-similar to addition to alkenes -pi bond becomes 2 sigma bonds -one molecule (triple bond-> double bond) or two molecules (triple bond-> single bond) may add -as with alkenes, addition of asymmetrical molecules (HX, H2O) can give Markovnikov or anti-Markovnikov products, but only if the addition is to a terminal alkyne
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Alkyne reactions (pics on pg 36)
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-HBr x2--> Markovnikov -HBr/ROOR x2--> anti-Markovnikov -HgSO4/H3O+--> Markovnikov (ketone) -1)Sia2BH 2)H2O2, NaOH--> anti-Markovnikov (aldehyde)
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Oxidation cleavage
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-besides addition reactions, double bonds can be involved in other reactions -both the pi bonds in a double bond break -C=C becomes C=O -mix of ketones and aldehydes (or carboxylic acids) are formed (CA is the oxidation product of the initial aldehyde under strongly oxidizing conditions)
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Oxidation cleavage reagents
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-warm or concentrated KMnO4--> carboxylic acid + ketone -ozonolysis: 1)O3 2)(CH3)2S--> aldehyde + ketone
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Oxidation/reduction
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-a molecule is oxidized or reduced when the following happens: -oxidation: loss of H2, gain of O, O2, or X2 -reduction: gain of H2, or H-, loss of O, O2, or X2 -neither: gain or loss of H+, H2O, HX (hydration/dehydration reactions, or addition of HX to double bonds) -oxidizing agents: Na2Cr2O7, CrO3/H2SO4 (H2CrO4), PCC, HNO3, HIO4, peroxides, KMnO4, O2, O3 -reducing agents: (CH3)2S, Zn, NaBH4, LiAlH4, SnCl2, H2
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Oxidation
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-the oxidation of a 1 alcohol yields an aldehyde first, then a carboxylic acid -the oxidation of a 2 alcohol yields a ketone, which cannot be oxidized further
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Combustion
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-combustion is the reaction of O2 with a molecule or atom -the molecule that reacts with O2 is being oxidized, while O2 is being reduced
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Reactions of carboxylic acids: neutralization (pics on pg 40)
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-like many other acids, carboxylic acids react with bases to form salts and water
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Esterification and other condensation reactions (pics on pg 41)
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-a condensation reaction joins two molecules by losing H2O -a condensation of a carboxylic acid and an alcohol forms an ester and water. this reaction is catalyzed by acid -the condensation of a carboxylic acid and an amine will form an amide and water -the condensation of a carboxylic acid and a thiol will form a thioester and water
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Acid hydrolysis (pics on pg 42)
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-all carboxylic acid derivatives can be hydrolyzed (under acidic conditions) back to a carboxylic acid -the reactivity of carboxylic acid derivatives decrease as shown below: (most reactive) acid chloride> anhydride> ester> amide> carboxylate (least reactive) -steric effects are also important in determining the rate of hydrolysis of carboxylic acid derivatives. small substituents such as H or CH3 result in faster hydrolysis while large ones (t-butyl, phenyl) result in slower hydrolysis
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Carboxylic acid derivatives interconversion (pics on pg 44)
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-the more reactive the carboxylic acid derivatives can be converted to the less reactive ones by reacting with alcohols to form esters or amines
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Saponification (basic hydrolysis) (pics on pg 45)
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-under acidic conditions the hydrolysis of an ester yields a carboxylic acid and an alcohol -under basic conditions, the hydrolysis of an ester yields the salt of the carboxylic acid and an alcohol
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Electrophilic Aromatic substitution (pics on pg 45)
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-electrophile substitutes for a hydrogen on the benzene ring -requires a very strong electrophile (a cation generated in-situ, often by addition of a lewis acid like AlCl3) -halogenation: Cl2/AlCl3 -sulfonation: SO3/H2SO4 -nitration: HNO3/H2SO4 -alkylation: CH3Cl/AlCl3 -acylation: Cl-C=0-CH3/AlCl3
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Proteins
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-building blocks: amino acids -there are twenty amino acids that make up human protein -they all have one carboxylic acid group, one amine (amino) group, one H, and one R group directly connected to a central alpha carbon. only the R group changes from one amino acid to the next -amino acid groups can be classified as non polar (glycine, alanine, leucine), polar (serine, cysteine), acidic (aspartic acid), and basic (lysine) -they can also be classified as branched (leucine) or unbranched (alanine)
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Specific amino acids
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-glycine: R=H -alanine: R=CH3 -leucine: R=CH2CH(CH3)2 -serine: R=CH2OH -cysteine: R=CH2SH -aspartic acid: R=Ch2COOH -lysine: R=(CH2)4NH2
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Zwitterion
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-when an amino acid is in water it will ionize, forming a zwitterion -has charged -NH3+ and COO- groups -forms when the -NH2 (basic) and -COOh (acidic) groups in an amino acid ionize in water -has equal + an - charges at the isoelectric point. the isoelectric point is the pH at which an amino acid exists as a zwitterion
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Condensation/hydrolysis
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-they key bond formed in joining the amino acid building blocks together is called a peptide bond -a peptide bond is an amide functional group (the result of condensing a carboxylic acid and an amine together) -peptide bonds are flat due to the shared electrons (resonance) between the O, C, and N atoms -a dipeptide consists of two amino acids joined together by one peptide bond -a polypeptide is many amino acids joined together -amino acid + amino acid ----condensation/hydrolysis---> dipeptide + water
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Levels of protein structure
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-once a polypeptide chain is formed in the cell (in a process called translation) it folds into a 3D structure that results in a "biologically active" protein -primary structure: the sequence of amino acids -secondary structure: the primary structure twists into an alpha helix, Beta pleated sheet, or triple helix held together by hydrogen bonds between the peptide bonds along the chain -tertiary structure: the secondary structure folds into a compact, 3D shape stabilized by interactions between the R groups of the amino acids (hydrophobic and hydrophilic interactions, salt bridges, hydrogen bonds, and disulfide bonds) -quaternary structure: two or more protein subunits combine to form a biologically active protein
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Denaturation
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-a change that disrupts the interactions between the R groups that stabilize the secondary, tertiary, or quaternary structure of a protein (heat, acids and bases, heavy metals, or agitation can cause denaturation) -a denatured protein is no longer biologically active
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Protein functions
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-proteins have many different functions, including structural (callagen), contractile (myosin), transport (hemoglobin), storage of nutrients (casein), hormonal (insulin), enzymatic (lactase), and protection (immunoglobulins) -enzymes and coenzymes (vitamins) can be either water soluble (C and B) or fat soluble (A, D, E, K)
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Carbohydrates
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-building blocks: monosaccharides -all sugar names end in -ose -monosaccharides consist of 3-6 carbon atoms, a carbonyl group (aldehyde or ketone) and several hydroxyl (alcohol) groups -aldoses are monosaccharides with an aldehyde functional group -ketoses are monosaccharides with a ketone functional group -monosaccharides exist as an open chain when dry or as a cyclic structure when in water -cyclic structures can exist as alpha (OH down) or beta (OH up) the inter convention between alpha and beta isomers is called mutarotation -monosaccharides that show inversion of configuration at a single chiral carbon are called epimers. glucose is an epimer of both mannose and galactose. epimerization is the conversion of one epimer into another
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Condensation/hydrolysis
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-the key bond formed in joining monosaccharides (simple sugars) building blocks together is called a glycosidic bond -a glycosidic bond is an ether functional group (the result of condensing two alcohols together) -a disaccharide consists of two monosaccharides joined together by one glycosidic bond -a polysaccharide (complex carbohydrate) is many monosaccharide units joined together -ex. starches, glycogen, cellulose -during digestion, glycogen is hydrolyzed into glucose, which is oxidized in our cells to provide our bodies with energy -monosaccharide + monosaccharide ----condensation/acid hydrolysis---> disaccharide + water
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Monosaccharides to disaccharides
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-glucose + glucose --> maltose + water -glucose + galactose --> lactose + water -glucose + fructose --> sucrose + water
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Lipids
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-are divided into simple and complex lipids -simple lipids are steroids an terpenes -they are not a result of a condensation reaction and are not made from fatty acids -complex lipids are waxes, triglycerides, and phospholipids -they result from the condensation of fatty acids and an alcohol to form an ester
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Complex lipids
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-building blocks: alcohol and fatty acids -waxes: long chain alcohol and fatty acid -triglycerides (fats and oils): glycerol and 3 fatty acids -phospholipids: glycerol, 2 fatty acids, phosphoric acid, and an amino alcohol -fatty acids are long chain carboxylic acids containing an even number of carbons, with the chain being 10-20 carbons long
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Fatty acids can be saturated or unsaturated
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-saturated: the hydrocarbon chain contains only C-C single covalent bonds. the general formula is CnH2nO2 -unsaturated: the hydrocarbon chain contains one (monounsaturated fatty acid) or more (polyunsaturated fatty acid) C=C double bonds
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Condensation/hydrolysis
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-the key bond formed in joining the alcohol and fatty acid building blocks together is an ester -esters are functional groups that result from the condensation of a carboxylic acid and an alcohol -waxes form one ester, triglycerides three esters, and phospholipids two esters and two phosphoesters -glycerol + 3 fatty acids ---condensation/hydrolysis--> triglyceride + 3 waters -while the acid hydrolysis of a tryglyceride yields glycerol and fatty acids, the basic hydrolysis of a triglyceride yields glycerol and the salt of fatty acids (soap) -triglycerides with saturated fatty acids are fats (solids at room temperature) triglycerides with unsaturated fatty acids are oils (liquids at rt) triglycerides are our long term reserve of energy, stored in our adipose tissue ( in cells called adipocytes) -phospholipids are the main component of cell membranes, making a "lipid bilayer"
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Soap molecules
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-contain a non polar end that dissolves in non polar fats and oils, and a polar end that dissolves in water -encapsulate grease with their non polar ends, and face the outside water environment with their polar ends -the structure is called a micelle and this is how soap dissolves grease in water
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Simple lipids
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-steroids and terpenes; these lipids are not made from fatty acids -steroids: compounds containing the steroid nucleus (4 rings fused together: 3 cyclohexane + 1 cyclopentane rings) -cholesterol is the most abundant steroid in the body -steroid hormones are derivatives of cholesterol (sex hormones- testosterone, estrogen, and progesterone-, adrenocortical hormones, and anabolic steroids) -terpenes: made of repeating isoprene units -steroids are derivatives of the triterpene squalene -vitamin A is an example of a terpene
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Nucleic acid
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-building blocks: nucleotides -nucleic acids are composed of nucleotides, which are linked together to form a polymer (DNA or RNA) -each nucleotide contains a base, sugar, and a phosphate group -the sugar is deoxyribose (in DNA) or ribose (in RNA) -the bases of DNA are adenine (A), guanine (G), cytosine (C), and thymine (T) -RNA also has A, G, and C, but instead of T RNA has uracil (U)
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Condensation/hydrolysis
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-there are multiple condensation reactions leading to a nucleic acid -first a sugar and a base condense to form a nucleoside -the key bond formed is an N-glycosidic bond (the result of condensing an amine and an alcohol together) -sugar + base ---condensation/hydrolysis--> nucleoside + water -next a nucleoside and a phosphate group condense to form a nucleotide -the key bond formed is a phosphoester (the result of condensing phosphoric acid and an alcohol together) -nucleoside + phosphate ---condensation/hydrolysis--> nucleotide + water -finally, nucleotides condense together to form a polymer, the primary structure of a nucleic acid -the key bond formed is another phosphoester (the result of condensing the 3'-OH group of the sugar in one nucleotide to the phosphate group on the 5'-carbon atom in the sugar of the next nucleotide) -nucleotide + nucleotide ---condensation/hydrolysis--> dinucleotide + water
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DNA
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-DNA is composed of two strands of nucleotides in which the bases of one strand are hydrogen bonded to the bases of the other -the pairs A-T and C-G are called complementary base pairs -A and T are joined by two hydrogen bonds while C and G are joined by three hydrogen bonds -the strands twist into a double helix -one strand of DNA is used as a template to produce a single strand of mRNA -the bases in the mRNA strand are opposite (complementary) to the bases in the DNA template, except that the base T is replaced with U -the mRNA contains a three letter code called a codon -each codon specifies for a particular amino acid
