Upon acceptance for publication in different journals following peer review, all journal articles had the same title of the selected preprints deposited at ChemRxiv, and at Preprints. Only in the case of preprint 8 first posted at Preprints, the title of the corresponding journal article was shorter.
The abstracts of the preprints published in ChemRxiv and the corresponding journal articles were the same in three out of five cases. The journal article deriving from preprint 2 specified that the article derived from interaction with the members of the Association of Environmental Engineering and Science Professors in a workshop organized at the 2017 association conference. The journal article published after preprint 4 includes two minor writing style changes.
The abstract of the preprints published in Preprints and the final published journal articles was the same in two out of five cases, specifically for preprints 6 and 9 and the corresponding journal articles. In the case of preprint 10 the abstract of the journal article [15] was significantly shorter than that in the preprint. The abstract of the final published article [16] is longer and slightly more informative than that of preprint7 , similarly to what happens for the abstract of the journal article [17] when compared to that of preprint 8 .
Little or no differences were found between the texts of the final journal articles and the preprints published in ChemRxiv months or weeks before. Preprint 1 even used the template of the subscription journal in which it was eventually published five months after the preprint. Interestingly, the study made freely accessible as preprint includes on each page the sentence “Submitted manuscript: confidential” [18]. Preprint 2 makes use of the template of the subscription journal in which it was published two months after the preprint as open access (OA), with a Table (Table 1) resulting of even higher readability (using colors) in the preprint [19] than in the peer reviewed article. In the case of preprint 3 , the final article published four months after the preprint in a OA journal includes three more references and slightly longer conclusions [20].
Preprints 4 and 5 do not use a journal template, but their content is virtually the same of the final published articles. Preprint 4 does not include page numbers [21] but embeds high resolution colored Figures and Schemes. Downloading the preprint from ChemRxiv, users would also download the Table of Contents graphics and the same 470-page long Supporting Information section found four months later in the final published article. When compared to the text of preprint 5 , the peer reviewed article published 16 days after the preprint [22], includes at the end of the article a brief “Post preprint addendum”, and five more references.
The latter preprint was uploaded, approved and published on the same day (October 17, 2018). The day before Angewandte Chemie published a manuscript [23] of a Swiss-German team reporting the invention of a similar method to obtain the molecular structure of microcrystalline molecular compounds via electron diffraction. The manuscript had been received by the journal editorial office on October 2, 2018.
Larger, though still not significant differences were noted between the selected preprints deposited at Preprints and the published journal articles. When compared to the text of preprint 6 , the final published article illustrates concepts through new research in a quickly developing field of chemistry published in the literature in the 20 months between the publication of the preprint and that of the journal article [24]. The final published article was virtually identical to preprint 7 , unless for a minor mistake in the sequential order of the Figures in the preprint that was corrected in the journal article [16].
When compared to preprint 8 , the final published article [17] had a substantially higher number of references (22 vs.17) and a longer and more informative conclusions section. In comparison to preprint 9 , the final published article [25] includes five new Schemes and one new Figure. The experimental section and the conclusions were identical.
The largest differences in the present analysis were noted between preprint 10 and the corresponding journal article [15]. The latter embeds a more succinct presentation, with only four Tables in the journal article vs. six in the preprint. Furthermore, the journal article includes both an elegant and highly explanatory image (Figure 1) displaying the experimental design and a new Figure (Figure 2) showing electron microscopic pictures of treated and non-treated orange peels. Both were absent in the preprint. Finally, the journal articles includes a richer conclusion section.
Published between 2018 and 2020, all selected preprints but one had more than 100 reads (unique views) by October 23, 2020. In general, the number of views was significantly higher for preprints published in ChemRxiv. For comparison, the most viewed preprint at Preprints among those selected herein had 928 views whereas the most viewed preprint at ChemRxiv had 60,352 views. In general, by the same date the most viewed preprint published by Preprints had 5,369 views (See at the URL: www.preprints.org/subject/browse/chemistry?filter=most_viewed).
The high number of reads for preprints posted at ChemRxiv was noted since the early days of the preprint server, when a manager of the OA programme of the ACS was “pleasantly surprised” [26] by the fact that by June 12, 2018, the 400 preprints posted had about 378,000 downloads/views. The trend continued, and two years later the editor of the online publishing platform remarked how preprints at ChemRxiv had been accessed “more than 10 million times, with upwards of 250,000 visitors to the site each day” [27].

Outlook and Perspective

Though exploratory and statistically non-significant, the analysis of 10 preprints selected from ChemRxiv and Preprints repositories and the respective published journal articles offers preliminary evidence that also in chemistry little difference exists between preprints and their final versions published as peer reviewed articles. Following studies and even experiments with reviewers involving the peer review process when editor of a prestigious medical journal, Smith in 2006 concluded that peer review “is a flawed process, full of easily identified defects with little evidence that it works” [28].
Chemistry scholars massively read preprints, with close to 13.5 million views for about 6,500 preprints posted on ChemRxiv by late October 2020. Furthermore, preprints deposited at ChemRxiv that had been cited 430 times in 2019 and 85 times in 2018, in 2020 started to be cited at fast rate with close to 1,050 citations in the first 10 months of 2020 (Source: Scopus, October 2020). By reading preprints, research chemists learn new methods and outcomes of relevance to their research several months ahead of time. Even in 2013, when virtually all chemistry journals were published on the internet, the average publication time (submitted to published time) for chemistry manuscripts was 9 months (and 4.5 months for submitted to accepted) [29].
Rather than striving to publish their work in journals of high journal impact factor, young chemistry researchers should be aware that the JIF is a poor statistical indicator imposed by a very small number of highly cited papers for which most papers published in high impact factor journals actually get fewer citations than indicated by the JIF [30]. In brief, by making their work freely and immediately accessible on the internet as preprints, chemistry scholars will rapidly reap the benefits of open science already demonstrated in closely related disciplines (life sciences and physics) in terms of enhanced citations, media attention, collaborations, job and funding opportunities [31]. Research chemists posting their research manuscripts on preprint servers, for instance, immediately enhance the visibility of their work. Also for chemistry scholars, the accurate measurement and wise evaluation of scientific output promoted by numerous scholars subscribing to the San Francisco Declaration on Research Assessment [32], today includes numerous other indicators beyond citations collectively called alternative metrics (“altmetrics”, for which even an international OA journal was established in 2018, Journal of Altmetrics). The number of reads (views) and downloads of each preprint, for example, is a common feature for both Preprints and ChemRxiv preprint servers, and a clear indication of interest of the scholarly community.
Table 4 . Average journal price by discipline in 2020. Top five ranking. [Source: Library Journal Periodicals Price Survey, 2020].