Medical Chemistry Seminar 2024 PDF

Week 8 Seminar 1 Medical Chemistry Seminar 2024 Unsaturated aliphatic hydrocarbons: alkenes, alkynes Department of Medical Chemistry UD Faculty of Medicine  Un...

Week 8 Seminar 1 Medical Chemistry Seminar 2024 Unsaturated aliphatic hydrocarbons: alkenes, alkynes Department of Medical Chemistry UD Faculty of Medicine  Unsaturated hydrocarbons triple (alkyne) bond(s). double (alkene) or ________ They contain one or more C-C ________ General formula: alkenes: CnH2n alkynes: CnH2n-2 What are the hybrization states of the carbons in alkenes and alkynes: sp2 sp (and sp3 for the non-double bonded carbons) What are their simplest representatives? 180° H H C C 120° H C C H H H Ethene ethene ethyne (an(ethylene) alkene) (acetylene) What can you say about the bond angles around the multiple bonds and the shapes of these molecules? Trigonal planar around the carbons; Linear; all 6 atoms in one plane all 4 atoms aligned  Nomenclature of alkenes CH3 CH2 = CH2 CH3 CH= CH 2 CH3 C= CH2 IUPAC: Ethene Propene 2-Methylpropene Common: Ethylene Propylene Isobutylene The parent is the longest continuous chain containing the double or triple bond. The ending is –ene for alkenes, -yne for alkynes. The carbons are numbered from the end closer to the first multiple bond. The position of the multiple bond is indicated by the number of the carbon the multiple bond follows placed in front of the parent name (1-hexene, 3-octyne).  Cyclo prefix + the name of the open-chain alkene containing the same number of carbons The double bonded carbons are 1 and 2. The rest of the carbons are numbered so that the first point of difference would get the lowest possible number. Naming enynes: compounds containing both double and triple bonds The chain is numbered from the end closer to the first multiple bond. If the multiple bonds are equidistant from the ends, the double bond has priority and the chain is numbered from the end closer to that one. We indicate the position of the double bond in front of the parent name, just like for alkenes, and place the position of the triple bond in front of the -yne ending. Naming alkenyl and alkynyl groups:  Draw structures for the following molecules: a. 3,3-diethyl-6-methyl-4-nonene b. 3-isopropyl-3,4-dimethyl-1,4-hexadiene c. cis-4-methyl-2-pentene d. trans-2,5-dimethyl-3-hexene a. 3,3-diethyl-6-methyl-4-nonene CH3 1 2 CH2 5 6 7 8 9 3 4 CH3-CH2-C-CH-CH-CH-CH2-CH2-CH3 CH2 CH3 CH3 b. 3-isopropyl-3,4-dimethyl-1,4-hexadiene H3C CH3 CH 1 2 3 4 5 6 CH2-CH-C-C-CH-CH3 H3C CH3 c. cis-4-methyl-2-pentene CH3 5 4 1 CH3-CH3 2 CH3 C=C H H d. trans-2,5-dimethyl-3-hexene 1 CH3 2 CH3- CH3 4 H C-C 5 6 H CH-CH3 CH3  Isomerism of alkenes Draw isomer structures for an alkene with the composition C5H10: - give IUPAC names for each isomer - identify the types of isomerism C5H10: a pentene CH3-CH2-CH2-CH-CH2 1-pentene Structural (positional) isomers; They differ in the position of the double CH3-CH2-CH-CH-CH3 2-pentene bond within the chain. CH3-CH2 CH3 C-C cis-2-pentene H H Stereoisomers or cis- trans (geometric) isomers CH3-CH2 H C-C trans-2-pentene H CH3 CH3 CH3-CH-CH-CH2 3-methyl-1-butene CH3 Structural (chain) isomers; CH3-CH2-C=CH2 2-methyl-1-butene They differ in connectivity of the carbons of the chain CH3 CH3-CH-C-CH3 2-methyl-2-butene  Isomerism and physical properties of alkenes Draw isomer structures for difluoroethene and give their IUPAC names. Classify the different types of isomers. Which of the isomers are polar? Composition: C2H2F2 dipole (polar) no dipole (nonpolar) F F F H C C C C H H H F cis-1,2-difluoroethene trans-1,2-difluoroethene geometrical (cis-trans) isomers H F C C dipole (polar) H structural isomers F 1,1-difluoroethene  Draw structures for each of the following molecules A. 3-methyl-2,4,6-octatriene B. 2,3-pentadiene C. 1,4,9-decatriene and classify them as a. isolated b. cumulated c. conjugated unsaturated compounds. A. 3-methyl-2,4,6-octatriene 1 2 3 4 5 6 7 8 CH3-CH-C-CH-CH-CH-CH-CH3 alternating double and CH3 single bonds: conjugated B. 2,3-pentadiene 1 2 3 4 5 double bonds follow each CH3-CH-C-CH-CH3 other: cumulated C. 1,4,9-decatriene 1 2 3 4 5 6 7 8 9 10 CH2-CH-CH2-CH-CH-CH2-CH2-CH2-CH-CH2 At least two single bonds separate double bonds: isolated  Reactions of alkenes What are the possible mechanisms for the activation of the double bond? Explain what happens in the two cases. Homolysis common in radical reactions Heterolysis reaction with electrophiles  Reactions of alkenes Explain the mechanism of the hydrohalogenation reaction of alkanes. Since the electrophilic reactant’s (H+) attack initiates the reaction which leads to breakage of the π- bond and addition of the H and the Cl to the alkene through the formation of two new σ-bonds, the mechanism is: electrophilic addition (AE).  Which isomer would not form in the reaction of 1-butene with HCl? Explain how electron displacement effects in the molecule answer for the regioselectivity of the reaction. Addition of HCl X 1-butene (+K-effect) acrylic acid (-K-effect) + Cl- + Cl- CH2-CH2-CH2-CH3 CH3-CH-CH2-CH3 CH2-CH2-COOH Cl Cl Cl 1-chlorobutene 2-chlorobutane 3-chloropropanoic acid Markovnikov’s rule: in the addition of HX or H2O to an alkene, H adds to the carbon of the double bond that has the greater number of hydrogens bonded to it Describe how double (a) Addition of hydrogenhalide, HX bonded carbons react C C + H–X C C with H X π bond σ bond 2 σ bonds (a)hydrogenhalide, HX to be broken to be formed (b)water (b) Addition of water (hydration) (c)Br2 (d)H2 C C + H2O C C H OH (e)with itself (polymerization) (c) Halogenation, X2 C C + X2 C C X X (d) Hydrogenation (reduction) C C + H2 C C H H (e) Polymerization initiator n C C C C n  Halogenation (bromination) of ethene Overall: Formation of a π-complex first, then a cation: π-complex bromocation product Due to steric considerations you learned about alkanes, the staggered conformation is preferred.  Hydrogenation Most alkenes react with H2 in the presence of a transition metal catalyst to give alkanes: - commonly used catalysts are Pt, Pd, Ru, and Ni Pt + H2 Cyclohexene Cyclohexane The process is called catalytic reduction or, alternatively, catalytic hydrogenation  Mechanism of the reaction - addition via a radical mechanism CH3 CH3 CH3 CH3 H H H H cis-1,2 dimethylcyclohexane H H (partially surface of the catalyst stereoselective)  Draw structures for the reactant and the product for each of the following reactions. Indicate the type of the reactions in each case. A. propane + Cl2 → B. propene + Cl2 → A. propane + Cl2 → chloropropane Halogenation - substitution CH3 CH2 CH2 Cl + HCl CH3 CH2 CH3 + Cl2 1-chloropropane CH3 CH CH3 + HCl Cl 2-chloropropane B. propene + Cl2 → 1, 2 dichloropropane Halogenation: addition CH3-CH-CH2 + Cl2 → CH3-CH-CH2-Cl Cl  Draw the structure for the reactant(s) and the products for each of the following reactions and name the products. Identify the mechanism of each reaction? A. 1-butene + HBr Pt/Pd B. propene + H2 initiator C. n isoprene A. 1-butene + HBr Br CH3-CH2-CH-CH2 + H+Br- CH3-CH2-CH-CH3 2-bromobutane Regioselective addition: electrophilic (AE) would not form Markovnikov’s rule ! CH3-CH2-CH2-CH2-Br 1-bromobutane  B. propene + H2 Pt/Pd CH3 CH CH2 + H2 CH3-CH2-CH 3 2 H propane Addition: radical mechanism initiator C. n isoprene CH3 CH3 initiator n CH2 C CH CH2 CH2 C CH CH2 n Isoprene polyisoprene (natural rubber) 2-methyl-1,3-butadiene Polymerization: radical or ionic mechanism depending on the initiator.  Give synthetic reactions of ethyne (acetylene). C 1) Ca + 2 H 2O HC CH + Ca(OH)2 C 2) 2 CH4 HC CH + 3 H2 Addition reactions of ethyne (acetylene): HgCl2 HC CH + H-Cl H2C CH - Cl vinil-klorid Vinyl-chloride Hg/HgSO4 HC CH + HOH [CH2 CH – OH] CH3 - CHO Vinyl-alcohol vinil-alkohol acetaldehyde The mechanism of the alkynes' hydrohalogenation and hydration reactions is also electrophilic addition (AE).  Give the chemical name and draw the structure of isoprene. Draw the shortened formula for a polymer of the molecule. 4 2 1 3 2-methyl-1,3-butadiene What is the isoprene rule? In most isoprene compounds the polymerisation is `head to tail΄ that is 1→4. HEAD TAIL polyisoprene  What do you know about terpenes (isoprenoids)? Give examples. Strictly speaking, terpenes are pure hydrocarbons with an oligo/poly-isoprene scaffold. Terpenoids/isoprenoids are derivatives of terpenes containing different functional groups and potentially undergone cyclization, saturation or desaturation of bonds. However, „terpene” is often used generally for all. Monoterpenes - 2 isoprene units; C10H16. geraniol, limonene, terpineol and myrcene, menthol Sesquiterpenes - 3 isoprene units; C15H24. (The sesqui- prefix means one and a half.) Classification humulene, farnesenes, farnesol. based on Diterpenes - 4 isoprene units; C20H32. isoprene-doublet cafestol, kahweol, cembrene, taxadiene, retinol, retinal, andphytol. (C10) units: Triterpenes - 6 isoprene units; C30H48. squalene, steroids, lupane, curcubitane. Tetraterpenes - 8 isoprene units; C40H64. phytoene, carotenoids, xantophylls. Polyterpenes Geraniol (C10) (+)-Menthol (C10) Limonene (C10) Humulene (C15) Has rose-like scent, used Minty scent and taste. Triggers cold Hoppy aroma of beer. Found in citrus fruit peels. in many perfumes receptors → cooling sensation. What is the name for the isoprenoid synthesis pathway? What are the names of the following intermediates of the pathway? What types of terpenes can be synthetized from them? Isopentenyl-pyrophosphate Dimethylallyl-pyrophosphate IPP DMAPP Geranyl-pyrophosphate (GPP) Farnesy-pyrophosphate (FPP) Which important molecule is synthetized from squalene? Cholesterol  What do you know about the structure and synthesis of carotenoids? They are tetraterpenes (C40). Synthesized by plants, fungi, microorganisms via condensation of mevalonate pathway intermediates. The ones containing an extended conjugated double bond sytem have color (→pigments). What is the name of the cyclic end groups in β-carotene? β-ionone rings What is the physiological significance of carotenoids for humans? β-carotene Vitamin A1  What is the molecular basis of vision? What is the photopigment in the human retina? Explain its structure and how that structure is connected to light sensing. The structure of rhodopsin - 11-cis-retinal is a cofactor of rhodopsin (bound to the protein through a Schiff base linkage) - Light-induced cis-trans isomerisation of retinal (photoisomerisation) → conformational change in the rhodopsin molecule → signal transduction → neuronal activation  MCQ1 Which compound exists as a cis-trans isomer pair? A. 2,3-dimethyl-2-butene B. 1,1, 2-trichloro-1-butene C. 1, 2-dichloro-1-butene D. 1,1-dichloro-1-butene E. 1-chloro-2-methylpropene  MCQ2 What is the correct mechanism of the reaction of ethene with water? A. Electrophylic substitution B. Elimination C. Nucleophylic addition D. Nucleophylic substitution E. Electrophylic addition  MCQ3 Which type of reaction is typical of alkenes? A. Polymerization B. Electrophylic addition C. Catalytic hydrogenation D. All of the above E. None of the above  MCQ4 What are the reaction products of 2-methyl-2-butene’s reaction with HCl? A. 2-chloro-3-methyl-butane B. 1-chloro-2-methyl-butane C. 2-chloro-2-methyl-butane D. 1-chloro-2-methyl-butane AND 2-chloro-3-methyl-butane E. 2-chloro-2-methyl-butane AND 2-chloro-3-methyl-butane  MCQ5 Which answer gives the correct reaction product of this chemical reaction: CH3-CH=CH2 + H2O → ? A. CH3-CH2-CH2-OH B. CH3-CH2-OH + CH4 C. HO-CH2-CH=CH2 + H D. CH3-CH-CH3 OH E. CH3-CH2-O-CH3  MCQ6 Which statement is wrong about terpenes? A. They are composed of 5-carbon isoprene units. B. The number of isoprene units in sesquiterpenes is 5. C. Their collective name is essential oils. D. They are biosynthesized from L-mevalonate E. Squalene is a representative of triterpenes  MCQ7 Choose the WRONG answer. Isopentenyl pyrophosphate….. A. is isomeric with dimethylallyl pyrophosphate. B. is involved in the synthesis of farnesyl phosphate. C. is involved in the synthesis of squalene. D. is a precursor for geranyl phosphate. E. is biosynthetized from isoprene  MCQ8 Which of the following compounds is NOT a terpene? A.β-carotene B. lycopene C.limonene D.phytol E.porfin  MCQ9 Which of the following transformations is photoisomerisation? A. Electrophilic substitution of alkanes. B. Isomerization of isopentenyl pyrophosphate into dimethylallyl pyrophosphate. C. Conversion of 11-cis-retinal to all-trans-retinal. D. Formation of vitamin A from β-carotene. E. Radical based substitution of alkanes.