Chm 219 Module 4 Exam | Questions & Answers (Verified) | Latest Update | Graded A+

1 CHM 219 MODULE 4 EXAM | QUESTIONS & ANSWERS (VERIFIED) | LATEST UPDATE | GRADED A+ Organohalides Correct Answer: Organic molecules contains Halogen atoms. Ex. Algae, Mollusk, sponges, can be industrially used - solvents, insecticides, herbicides, cleaning fluids, fire retardants, refrigerants. Can also be used as inhaled anesthetic. More important in organic chemistry because of theur reactivity. Two of the most important reaction types typical of organic Halides are.... Correct Answer: Substitution Elimination Substitution Reaction Correct Answer: Replacing the halogen in a molecule with another atom or functional group. Elimination 2 Correct Answer: Removes the halogen and hydrogen atoms from the original substrate molecule creating an unsaturated compound. Alkyl halide Correct Answer: Aliphatic hydrocarbons that possess one or more halogen atom substituents. Aryl Halides Correct Answer: Aromatic hydrocarbons (benzene rings) with one or more halogen atoms attached to the ring. Steric Bulk Correct Answer: Structural substitution surrounding any carbon atom that bears a halogen. Methyl, primary, secondary, tertiary. Primary Alkyl Halide Correct Answer: Only on e carbon is directly attached to the carbon bearing the halogen. Secondary Alkyl Halid Correct Answer: Two carbons directly attached to the carbon ring bearing the halogen Tertiary Alkyl Halide Correct Answer: Three carbons are directly attached to the carbon bearing the halogen 3 Methyl halide Correct Answer: Only hydrogen atoms attached to the carbon bearing the halogen X Correct Answer: Symbol for generic halogen Polarization of C-H bond Correct Answer: Carbon will be electron-deficient and thus hold a slight positive charge and slight negative charge on the halogen Nucleophilic substitution reaction Correct Answer: Halogen is replaced (substituted by) a new atom or functional group. Abbreviated Sn Functional Group Interconversion Correct Answer: When one type of functional group (alkyl halide) is converted to another by substitution. Substrate Correct Answer: Molecule on which the substitution occurs. Leaving group 4 Correct Answer: Atom or group of atoms that is replaced by another when substitution occurs Nucleophile Correct Answer: A chemical species that seeks positive charge due to the presence of one or more lone pairs present on an atom in the nucleophile Typical Nucleophiles - O,N,S Nucleo = nucleus/positive charge Phile = love There can be negatively charged nucleophiles (more reactive) or neutral nucleophiles. Generic presentation of nucleophile substitution reaction Correct Answer: Nucleophile: + Substrate-Leaving group — nucleophile-substrate + leaving group Unreactive in nucleophilic substitution reactions Correct Answer: Aryl and vinyl halides. Substrates in which the halogen is attached to a C that is a part of a multiple bond. Mechanism Correct Answer: Term used by organic chemists to describe and explain how reactions happen at the molecular level. 5 Also called "roadmaps" because they describe the stepwise formation of products from the reactant molecules. Two Main Types of Nucleophilic Substitution REactions Correct Answer: Sn1 and Sn2 Sn2 Correct Answer: -single step (concerted) -nucleophile attacks from the backside of the C-L bond. Nucleophile uses a lone pair of electrons to begin making a bond to the carbon. Simultaneously the bond between the C and the L begins to break. "Backside attack" -Transition state: nucleophile and leaving group are both partly attached to substrate. -L departs from the substrate with the pair of electrons from the C-L bond and nucleophile is fully bonded to the C -Inversion of the tetrahedral geometry occurs. *increasing the concentration of either the nucleophile or substrate will increase the rate of the reaction *2 is used becuae nucleophile and substrate are involved in the only step (key step) *methyl and primary alkyl halide react this way more easily FActors that influence the mechanistic path... of Sn2 Correct Answer: -Strength of the nucleophile - SN2 depends on a strong Nucleophile, the more negative, the stronger. 6 -Size of nucleophile - larger are more efficient -Electronegativity of the Nucleophilic atom - the more electronegative, the less nucleophilic -Solvent chosen - they are polar and require polar solvents ; best solvents are polar aprotic solvents Sn1 Correct Answer: -two steps -Step 1 - Leaving group leaves first. C-L bond breaks and produces 2 ionic products: carbocation intermediate and a leaving group anion (this step is energy intensive and very slow) known as the rate determining step (RDS) -Step 2 - nucleophile attacks the carbocation intermediate, using a lone pair to form a covalent bond. *no inversion of tetrahedral geometry *produces 50:50 enantiomers. *secondary and tertiary typically react this way Factors that influence the mechanistic path of... Sn1 Correct Answer: -nucleophile size, strength , concentration and electronegativity have no effect -solvent chosen - polar protic solvents - they can donate H bonds becuase they have - OH, -NH, or -SH froup as part of their structure. 7 Elimination reaction Correct Answer: When the structure of the alkyl halide substrate contains one or more hydrogen atoms attached to the carbon adjacent to the carbon bearing the leaving group. Halogen atom is removed, along with H atom from the adjacent C atom to create an alkene. Product - ALKENE -nucleophile acts as a base and removes a H (proton) from a C adjacent to the C bearing the halogen , this C is known as the Beta C and the H associated are called Beta Hydrogens -The C bearing the leaving grou is the alpha C and associated H are alpha H Dehydrohalogenation Correct Answer: When the reaction occurs specifically on an alkyl halide substrate. Both H and Halogen are being eliminated from the substrate molecule. E2 Correct Answer: -one step -biomolecular -Nucleophile acts as a base and removes the beta H from the beta C, at the same time the electrons from the C-H bond come down tot for a C=C bond and break the carbon halogen bond, releasing a halide ion. 8 E1 Correct Answer: -several steps -alkyl halid first undergoes dissociation from the carbocation intermediate. -once formed the carbocation intermediate undergoes elimination by the nucleophile (acting as base) removing a Beta H from a beta C to form the C=C Primary Alkyl Halide (RCH2X) Correct Answer: Will react by an Sn2 pathway if a good nucleophile (I-, Br-, RS-, NH3, or CN-) is used. There will be increasing amounts of elimination product from an E2 pathway as the basicity of the nucleophile increases (HO-, RO-). No Sn1 or E1 pathways are possible for primary substrates. Secondary Alkyl Halide(R2CHX) Correct Answer: While all four mechanistic pathways are possible, typically these substrates will react by both Sn2 (when weak bases are used) and E2 (when strong bases are used) pathways to give a mixture of substitution and elimination products. Tertiary alkyl halide (R3X) Correct Answer: Will react by an E2 pathway when a strong and/or bulky base is used as the nucleophile. When a weak nucleophile is used (or under acidic conditions) a mixture of substitution and elimination products will form by Sn1 and E1 mechanisms. No Sn2 pathway is available for tertiary substrates.