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Paul Rablen

Edmund Allen Professor of Chemistry

Chemistry & Biochemistry


  2. Phone: (610) 328-8341
  3. Science Center 292


NIH Postdoctoral Fellow, Yale University, Department of Chemistry
Ph.D., Organic Chemistry, Yale University
M.A., Organic Chemistry, Columbia University
B.A., Chemistry, Haverford College


CHEM 010 HN, CHEM 022, CHEM 122, CHEM 032.


Research in my laboratory focuses on fundamental questions about the relationship between structure, stability, and reactivity in organic compounds, and on questions about the mechanistic pathways of organic reactions. These questions are pursued through the use of ab initio molecular orbital calculations. These quantum mechanical calculations yield quite accurate predictions for the energies, geometries, and spectroscopic properties of stable compounds, intermediates, and even transition structures. There also many collaborations with other laboratories both at Swarthmore and at other institutions.

Recent specific topics have included:

  • What electronic factors affect the relative amount of ortho- and para-substituted products in electrophilic aromatic substitution reactions.
  • A computational protocol for determining Hammett substituent constants sp, sm, s+p, s+m, sp, and sm.
  • How the distribution of alkyl groups affects the stability of allyl and pentadienyl carbocations.
  • How the multistep carbocation rearrangement involved in the transformation of caryolanol to isoclovene takes place.

Recent Publications

(undergraduate researchers marked with *)

Rachii, D.; Caldwell, D. J.; Kosukegawa, Y.; Sexton, M.; Rablen, P. R.; Malachowski, W. P. “Ni-Catalyzed Enantioselective Intramolecular Mizoroki−Heck Reaction for the Synthesis of Phenanthridinone Derivatives” J. Org. Chem. 2023, 88, 8203-8226.

Meier, R. J.; Rablen, P. R. “Group Contribution Revisited: The Enthalpy of Formation of Organic Compounds with “Chemical Accuracy Part IV” Thermo, 2023, 3, 289-308; DOI: 10.3390/thermo3020018.

Rablen, P. R.; Yett, A.* “The relative favorability of placing substituents ortho or para in the cationic intermediate for electrophilic aromatic substitution” J. Phys. Org. Chem., 2022, 35, e4457; DOI: 10.1002/poc.4457, 1-11.

Yett, A.;* Rablen, P. R. “A G4 approach to computing the Hammett substituent constants sp, sm, s–, s+, and s+m” J. Phys. Org. Chem., 2022, 35, e4436; DOI: 10.1002/poc.4436, 1-14.

Paley, R. P.; Hejna, B. G.;* Quevedo, R. E.;* Wong, A. R.;* Dow, N. W.;* Murphy, J. S.;* Choi, S.;* Yu, M.;* Rablen, P. R.; Pike, R. D. “N-Oxazolidinoyl Diene Iron(0) Tricarbonyl Complexes: Preparation by Diastereoselective Complexation and Synthetic Applications” Organometallics 2022, 41, 2188-2219, DOI: 10.1021/acs.organomet.2c00272.

Barrows, R. D.; Dresel, M. J.; Emge, T. J.; Rablen, P. R.; Knapp, S. “Stereoelectronic Features of a Complex Ketene Dimerization Reaction” Molecules 2022, 27, 66-76.

Banert, K.; Hagedorn, M.; Heck, M.; Hertel, R.; Ihle A.; Müller, I.; Pester, T.; Shoker, T; Rablen, P. R. “Synthesis of Trialkylamines with Extreme Steric Hindrance and Their Decay by a Hofmann-like Elimination Reaction” J. Org. Chem. 2020, 85, 13630-13643.

Barrows, R. D.; Hammill, J. T.; Tran, M. C.; Falade, M. O.; Rice, A. L.; Davis, C. W.; Emge, T. J.; Rablen, P. R.; Guy, R. K.; Knapp, S. “Evaluation of 1,1-cyclopropylidene as a thioether isostere in the 4-thio-thienopyrimidine (TTP) series of antimalarials” Bioorganic & Medicinal Chemistry 2020, 28, 115758.

Wiberg, K. B.; Rablen, P.R. “Re-Examination of Some Carbocations.  Structures, Emergies, and Charge Distributions.” J. Org. Chem. 2020, 85, 11741-11749.

Rablen, P. R. “A Procedure for Computing Hydrocarbon Strain Energies Using Computational Group Equivalents, with Application to 66 Molecules” Chemistry 2020, 2, 347-360; doi:10.3390/chemistry2020022.

Wiberg, K. B.; Rablen, P. R. “Increase in Strain Energy during Conversion of []Fenestrane to []Fenestrane: a Method for Estimating the Heats of Formation of Hydrocarbons and Their Derivatives from Ab Initio Energies” J. Org. Chem. 2020, 85, 4981-4987.

Beckmann, P. A.; Rablen, P. R.; Schmink, J.; Szewczyk, S. T.; Rheingold, A. L. “Concomitant Polymorphism in an Organic Solid: Molecular Structure, Crystal Structure, and Intramolecular and Intermolecular Potential Contributions to tert-Butyl and Methyl Group Rotation” ChemPhysChem 2019, 20, 2887-2894.

Le, N. T. L.; Just, J.; Pankauski, J. M.; Rablen, P. R.; Thamattoor, D. M. "The Ring Expansion of Alkylidenecarbenes derived from Lactams, Lactones, and Thiolactones into Strained Heterocyclic Alkynes:  A Theoretical Study" Molecules 2019, 24, 593-618.

Woodside, A. J.;* Smith, M. A.;* Herb, T. M.; Manor, B. C.; Carroll, P. J.; Rablen, P.R.; Graves, C. R. "Synthesis and Characterization of a Tripodal Tris(nitroxide) Aluminum Complex and Its Catalytic Activity toward Carbonyl Hydroboration" Organometallics 2019, 38, 1017-1020.

Wiberg, K. B.; Rablen, P. R. "Atomic Charges" J. Org. Chem. 2018, 83, 15463-15469.

Wiberg, K. B.; Rablen, P. R. "Methoxymethane C–O Bond Strengths:  Do Their Changes Result from Hyperconjugation or Polar Effects?" J. Phys. Chem. A 2018, 122, 6021-6025.

Wiberg, K. B.; Rablen, P. R.; Baraban, J. H. "Butadiene and Heterodienes Revisited" J. Org. Chem., 2018, 83, 8473-8482.

Rablen, P. R. "Acid-catalyzed conversion of caryolan-1-ol to isoclovene:  a computational investigation of the multi-step carbocation rearrangement" Tetrahedron 2018, 74, 3781-3786.

Kirsh, J. M.;* Woodside, A. J.;* Manor, B. C.; Carrol, P. J.; Rablen, P. R.; Graves, C. R. "Synthesis and Characterization of (pyNO–)2GaCl: A Redox-Active Gallium Complex" Inorganics 2018, 6, 50; doi: 10.3390/inorganics6020050.

Nathanael, J. G.; Gamon, L. F.; Cordes, M.; Rablen, P. R.; Bally, T.; Fromm, K. M.; Giese, B.; Wille, U. "Amide Neighbouring Group Effects in Peptides:  Phenylalanine as Relay Amino Acid in Long-Distance Electron Transfer" ChemBioChem 2018, 19, 922-926.

Rablen, P. R.; Perry-Freer, N. A.* "How the arrangement of alkyl substituents affects the stability of delocalized carbocations" J. Org. Chem. 2018, 83, 4024-4033.

Barrow, R. D.; Blacklock, K. M.; Rablen, P. R.; Khare, S. D.; Knapp, K. "Computational Assessment of Thioether Isosteres" J. Mol. Graph. Model. 2018, 80, 282-292.