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Paper text:
the reactant is resorcinol , 
 a highly activated 
 aromatic molecule that reacts quickly and efficiently by electrophilic 
 aromatic substitution under acidic conditions .
each student prepares 
 a solution of resorcinol ( 0.60 mmol ) in d2o ( 1 ml ) containing 
 h2so4 ( 20 l ) .
one reaction solution 
 is analyzed by h nmr spectroscopy , and the other solution 
 is used in the iodination reaction ( as the reaction mixture ) .
students prepare another solution of resorcinol in acidic d2o that is not refluxed as a ( nondeuterated ) control .
students 
 conduct iodination of resorcinol at room temperature by adding a dilute 
 solution of molecular iodine and potassium iodide in ethanol simultaneously 
 to two vials , one containing the reaction mixture and the other containing 
 the ( nondeuterated ) control . the reaction progress 
 is monitored visually via the disappearance of iodine color in the 
 reaction solutions due to the formation of 2-iodoresorcinol and 4-iodoresorcinol . 

the kinetic isotope effect of the iodination reactions is quantified 
 by analysis of uv  vis spectroscopic data provided to students .
a solution of sulfuric acid in d2o can be prepared 
 in advance for students to use .
no safety information is available 
 for resorcinol - d5 , but similar safety 
 concerns are reasonably expected .
the solution of iodine / iodide in ethanol may be corrosive and should 
 be handled with care .
the iodination products of resorcinol , including 
 2-iodoresorcinol , are harmful if swallowed , inhaled , or absorbed through 
 the skin .
students should wear proper personal protective equipment 
 at all times when performing this experiment , including gloves , a 
 lab coat , and safety goggles .
chemical manipulations are recommended 
 to be done in an appropriate fume hood if possible .
this experiment has been completed once in a laboratory session 
 of 3 h by a total of 15 first - semester undergraduate organic chemistry 
 students .
h bonds in resorcinol did not undergo significant 
 h  d exchange in refluxing d2o in a time frame reasonable 
 for use in a classroom setting .
however , when d2o and sulfuric 
 acid were mixed together , the concentration of d3o in solution and subsequent reactivity were greatly increased . 
 to conduct the reaction , a microscale reflux apparatus , consisting 
 of a small vial containing a spin vane ( a boiling chip would be sufficient ) 
 with a reflux condenser , was heated on a hot plate .
the reaction typically 
 reached equilibrium within 30 min of heating , after which no further 
 net deuteration would occur .
the appearance of the reaction mixture 
 did not change over the course of the experiment .
d exchange at the 2- , 4- , and 
 6-positions on the ring ( scheme 1 ) .
this result 
 was in accord with a typical eas mechanism involving slow addition 
 of d+ to the aromatic ring to form an intermediate arenium ion followed 
 by rapid elimination of the proton .
though there was a negligible 
 kinetic preference for elimination of the proton over the deuteron , 
 the high concentration of deuterium in solution resulted in preferential 
 formation of the trideuterated species .
the alcohol protons were also 
 exchanged , but this had no effect on the outcome of the experiment .
the extent 
 of deuteration was determined by 
 integrating the remaining proton at the 5-position and comparing it 
 to any remaining proton signals ( figure 1 ) . 

this proton was meta to the activating hydroxyl groups 
 on the ring and thus not activated toward electrophilic exchange . 

as a result , deuterium incorporation at this position was negligible 
 during the course of the experiment .
the nmr signal associated with 
 this proton collapsed from a triplet into a broad singlet , providing 
 strong evidence that neighboring protons were exchanged with deuterium . 

d coupling in the spectrum , 
 despite deuterium being nmr active ( i = 1 ) , typified 
 important differences between h  h and h  d spin 
spin 
 coupling and can provide an introduction to more advanced nmr concepts 
 such as the magnetogyric ratio .
the spectrum was used as an effective 
 explanation of electrophilic aromatic substitution trends due to the 
 clear distinction between near complete exchange at the positions ortho and para to the activating hydroxyl 
 groups and very minor exchange at the meta position . 

h nmr spectra of resorcinol prior to ( left ) and after 
 ( right ) h  d exchange . by adapting the procedure from a previous work , students visualized the kinetic isotope effect 
 by adding 
 a dilute ethanolic solution of iodine and sodium iodide to the reaction 
 mixture containing deuterated resorcinol and a control mixture of 
 resorcinol and sulfuric acid in d2o at ambient temperature 
 ( scheme 2 ) .
before addition of the iodine solution , 
 the deuterated mixture and control ( nondeuterated ) mixture were clear , 
 nearly colorless , and visually indistinguishable .
after initial addition 
 of the iodine solution , both the deuterated mixture and control mixture 
 were translucent and dark orange - red in color .
the color faded , and 
 the solutions clarified as the iodine reacted with the resorcinol . 
 in each case , after completion of the reaction , the solution was clear 
 and very light yellow in color , indicating that a trace amount of 
 unreacted iodine may remain . in the control experiment ,
the iodine color of the solution 
 faded 
 much more rapidly ( i.e. , a change was apparent within 5 min ) compared 
 to the deuterated example , and the reaction was nearly complete after 
 approximately half an hour . comparatively , the isotopically labeled 
 resorcinol - d5 reacted much more slowly , 
 and the reaction remained incomplete after well over an hour .
the 
 concentration of iodine remained consistently higher in the vial containing 
 deuterated resorcinol throughout the duration of the experiment , providing 
 a qualitative visual representation of the comparative reactivities 
 of each substrate .
the effect was best observed when the experimental 
 and control reactions were conducted side - by - side and a student could 
 observe both results simultaneously .
while reaction time and the concentration 
 of iodine varied somewhat from student to student , the trend was very 
 clear in each case and the effect was easily visualized . the 
 kinetic isotope effect kh / kd of the iodination reaction was also determined 
 quantitatively
the reaction of iodine with resorcinol under the aforementioned 
 conditions was found to be second - order overall , providing an excellent 
 opportunity to quantify the kie by monitoring the uv  vis absorption 
 spectrum of iodine as it reacted .
however , because a significant amount 
 of time was required to collect sufficient uv  vis data and 
 the outcome appeared to be somewhat sensitive to minor variances in 
 preparation , previously obtained data were given to students for interpretation . 
 when 1/[i2 ] versus time was plotted for the control and 
 experimental conditions and the slopes of these plots were compared , 
 a kh / kd of 
 approximately 3.4 was calculated .
representative uv  vis absorbance 
 data for this experiment are in the supporting 
 information .
a key aspect 
 of this experimental methodology is its adaptability 
 to fit the target audience .
this experiment was primarily utilized 
 as part of the lab curriculum for first - semester undergraduate organic 
 chemistry students . prior to conducting the experiment , most students 
 only had a cursory understanding of isotopes and their effect on chemical 
 reactivity .
students were introduced to the concepts of electrophilic 
 aromatic substitution , isotopic exchange , and the kinetic isotope 
 effect as part of the required reading before the experiment . by performing 
 the experiment ,
students were able to comprehend better eas and isotopic 
 exchange . using h nmr spectroscopy
, they were able to 
 familiarize themselves with the instrumentation and its utility in 
 characterizing such isotopic exchange reactions .
additionally , they 
 interpreted uv  vis absorbance data to quantify the kinetic 
 isotope effect of the iodination reaction and rationalize its rate 
 and mechanism .
after the experiment , post - lab write - ups indicated 
 that all students had a significantly greater understanding of eas 
 and the kinetic isotope effect , and many were interested in the potential 
 applications of the chemistry , including the production of deuterated 
 drugs .
the materials given to students , including introductory material 
 as well as pre - lab and post - lab questions , are provided in the supporting information . as a secondary 
 project ,
the deuteration and iodination reactions 
 were successfully performed and the results interpreted by ambitious 
 high school students looking to gain experience with undergraduate - level 
 chemistry .
these students had previous experience with chemistry courses 
 but were not familiar with isotopic substitution reactions or their 
 effects .
while some of the more complicated aspects of the transformation 
 were omitted , the fundamental aspects of isotopic exchange could be 
 understood and demonstrated experimentally .
isotope effects were explained 
 by comparing the physical properties of d2o and h2o ( slightly different molar masses and densities ) , as well as by 
 monitoring the iodination reaction visually . in each case , students 
 saw firsthand that isotopically substituted compounds often have very 
 similar physical properties but can be differentiated through experimentation . 

this methodology is amenable to a diverse audience of chemistry students 
 and educators , with the complexity of the material highly adaptable 
 to the desired outcome .
an efficient laboratory experiment 
 has been developed for undergraduate 
 students to conduct hydrogen  
 deuterium ( h  d ) exchange 
 of resorcinol by electrophilic aromatic substitution using d2o and a catalytic amount of h2so4 . 
 the resulting 
 labeled product is characterized by 1h nmr . 
 students also 
 visualize a significant kinetic isotope effect ( kh / kd  3 to 4 ) by adding 
 iodine tincture to solutions of unlabeled resorcinol and the h  
 d 
 exchange product . 
 this method is highly adaptable to fit a target 
 audience and has been successfully implemented in a pedagogical capacity 
 with second - year introductory organic chemistry students as part of 
 their laboratory curriculum . 
 it was also adapted for students at the 
 advanced high school level .